Table of Contents
- 1. Part One: General Concepts
- 1.1. Introduction
- 1.2. Videos
- 1.3. What do you want from a trigger job?
- 1.4. Thoughts about gunsmithing
- 1.5. Required tools
- 1.6. Removing the sideplate
- 2. Part Two: Working with Springs
- 2.1. Two important springs
- 2.2. Understanding spring strength and light strikes
- 2.3. Springs for duty guns
- 2.4. Polishing internal parts
- 2.5. J-frames vs larger frames
- 2.6. Working with leaf mainsprings and the strain screw
- 2.7. Single action safety issues: light triggers and push off
- 2.8. Primer sensitivity
- 2.9. Double action trigger weight
- 2.10. Testing spring changes
- 3. Appendix
- 3.1. Reference materials
- 3.2. Rimfire vs centerfire
- 3.3. Despurred and lightened hammers
- 3.4. Push-off
- 3.5. Working on the single action
- 3.6. Firing pins
- 3.7. Details on primer sensitivity
- 3.8. Modifying springs
- 3.9. Measuring mainspring strength
1 Part One: General Concepts
Part one covers general concepts about gunsmithing and about working on revolvers. Even if you do not plan to work on revolvers, this part may be useful since these concepts will help you communicate more effectively with your gunsmith.
This article is intended for anyone who wants to improve the trigger on their Smith & Wesson revolver. I frequently see questions on internet forums about how to do a trigger job on a revolver, and I see many answers recommending aftermarket spring kits. But working with revolver springs is trickier than it might appear.
The actual process of replacing springs is not too difficult, but getting a good trigger pull without compromising reliability often takes more effort. So while some people swap springs and get good results, many others get a less satisfactory outcome. I am happy for those who get good results, but their success often involves a good amount of luck. The goal of this article is to offer background knowledge that will reduce the amount of luck required.
This article is not a tutorial about how to work on revolvers or about which specific springs to use. Instead, it will discuss general knowledge about gunsmithing and about how revolvers work. This background knowledge will help you avoid problems and help you resolve issues if they do occur. This article is specifically about Smith & Wesson revolvers, but many of the principles apply to any double action revolver.
Part one of this article, which you are now reading, focuses on general concepts. Part two addresses details about working with revolver springs. And the appendix has in depth details about many common but esoteric questions.
This document is provided solely for informational purposes. The author is not responsible for any work you do on firearms.
More importantly, if you are working on firearms, you should be proud of the quality of your work, and eager to take responsibility for it. If you do not feel this way, then you should leave gunsmithing to the professionals.
1.1.2 The author is not compensated for endorsements.
I do not have any endorsement agreements, and I am not compensated in any way for endorsements in this article. My recommendations are based solely on my own opinions about products that I use and like.
If you are not familiar with the internal workings of Smith & Wesson revolvers, then reviewing some short videos may help clarify the terminology in this article.
I think the videos below are useful, but they are still far from perfect. I have chosen these videos partly because they have good production standards, and they include clear and well lit close-ups of the inside of revolvers. But I do not fully endorse the content of these videos, and they should be viewed with a critical eye. For example, the video from MidwayUSA is quite over optimistic about the ease and likely success of installing revolver springs. I like the video from Jerry Miculek better, but it still does not address the potential pitfalls of changing springs. In fact, I think the optimism of these videos has contributed to the problem of people changing springs without understanding the consequences. But overall, there is useful information in these videos, and they are worth watching if you are not familiar with the internals of revolvers.
1.3 What do you want from a trigger job?
If you are reading this article, you are probably interested in making improvements to a revolver. But before I discuss the internal mechanics of revolvers, I want to talk about the end goals of doing a trigger job. Whether you decide to do the work yourself, or you decide to go to a qualified gunsmith, having clear goals will help you have a successful outcome.
The first question to consider is: do you want to lighten the single action, or do you want to make the double action easier to control, or both? Many steps in tuning a revolver only affect one part of the action, so if you only care about the single action or the double action, then that can determine which tuning steps will be important to you.
Also, there are two different aspects of the trigger pull which can be considered separately: the weight and the feel. The weight can be measured and quantified using a trigger scale, while the feel is more subjective. But the feel can still be qualified using specific terms like creep, grittiness and overtravel. In general, changing springs will change weight of the trigger, but springs do not change the feel.
In the next sections, we will discuss how both weight and feel relate to the single action and double action on revolvers.
1.3.1 Single action
Smith & Wesson revolvers are widely known for the excellent feel of their single action. This feel comes from the unusual design of the single action engagement between the hammer and trigger. The hammer notch on a Smith & Wesson revolver is only about six thousandths of an inch deep, which is far smaller than the hammer engagement on most firearms. This design gives the single action trigger on S&W revolvers an extremely crisp break with no movement before the break.
However, on some Smith & Wesson revolvers, the single action weight is about 4 lb, and some shooters find this weight a bit heavy. If your only goal is to reduce the single action pull to about 3 lb, then this goal can often be achieved just by changing the rebound spring. This spring change is described in the section about the two important springs.
On the other hand, if there is a problem with the feel of the single action on your revolver, then you should talk to a gunsmith. For example, if the trigger moves a bit before the hammer drops, then there is an issue with the shape of the hammer notch or the single action sear. This issue is uncommon, but it can occasionally happen. Since the single action engagement areas on a S&W revolver are extremely small, repairs to these areas are best left to a gunsmith.
1.3.2 Double action
If you are interested in having a more controllable double action trigger, then you need to think about the feel as well as the weight. When people talk about double action triggers, they often talk primarily about weight, and about how light a trigger should be. This focus on weight makes sense, since weight is easy to measure and compare, but weight does not really tell the whole story. There are many important aspects to a good double action trigger, and weight is just one of them.
So let's talk about the feel of a good double action trigger. First, it should be smooth. There should be no bumps, catches, or gritty feeling. And the pull should be even and not get steadily heavier as the trigger moves back. If the trigger pull is bumpy or uneven, it is difficult to pull the trigger smoothly without disturbing the sights. Also, you need to consider how the trigger feels when it resets to the forward position after firing a shot. The forward movement of the trigger is called the "trigger return," and the return should be brisk and smooth. If you want to fire double action rapidly, then the trigger return is very important.
Some people say that for double action, smoothness is more important than weight. I mostly agree with that statement. A good double action must be smooth, and it does not need to be extremely light, but it also should not be too heavy. A very smooth double action often feels lighter than it really is, and a rough double action is difficult to shoot well, even if it is quite light.
So how do you get a smooth double action? The answer is that smoothness comes from polishing the action. Changing springs will affect the weight, but it will not change a gritty feel. The smoothness of factory revolvers varies considerably from one gun to the next, but most revolvers require some internal polishing to have a good double action.
1.4 Thoughts about gunsmithing
Before I discuss more specific details about revolvers, I want to discuss four general thoughts about gunsmithing.
1.4.1 Check all mechanical safety functions
If you make any modifications to a firearm, you are responsible for the safety of the firearm. You must understand the safety mechanisms in the firearm, and you must confirm that all the safety features still work correctly after your changes are complete.
1.4.2 Duty guns should be worked on by experts
If you want to make changes to a gun, then you should think about its intended purpose. If the gun will be used for defense or protection, then I would call it a duty gun, and I would consider reliability to be the highest priority. I strongly recommend that duty guns should be worked on by experts. It is worth the extra cost to have an expert make certain that any necessary changes are done correctly. In some cases, a modified gun may seem to work properly, but subtle issues can cause reliability problems down the road. An expert's experience allows him to identify and avoid these issues. And there is just no substitute for experience when you need things done right the first time.
Note that I am not saying that home gunsmiths should never work on duty guns. But if you are going to work on a duty gun, you should have enough training and experience to be certain that the work is done correctly. If you are still learning about gunsmithing, then you should practice on guns that will only be used for recreation and training.
1.4.3 Reversible and non-reversible changes
If you are making changes to firearm, consider whether the changes will be reversible. If you install aftermarket parts in a firearm, and you put all of the original parts aside, then those changes are reversible. If you do not like the results, you can just put the original parts back, and the gun is back to original condition. If you stone, file or polish any of the original parts, then there is no way to undo the changes.
Whenever possible, it is best to make reversible changes. If you need to modify an original part, you should consider whether to buy a replacement part and modify that one instead. I personally have bought replacement parts just so that I could put the original parts aside, and I have never regretted that decision.
When people suggest changing springs in a revolver, they often point out that swapping the springs is a reversible change, so there is no reason not to try it. There is some truth to this viewpoint. But I usually find that stoning and polishing are also required to get a good double action trigger. And stoning parts is a very non-reversible change. So if you want to only make reversible changes, you need to consider whether reversible changes will really deliver good results.
1.4.4 Revolvers are hand fit guns
From a gunsmithing perspective, guns can be broadly divided into two groups: guns where new parts drop in, and guns where most parts need to be fitted. On many modern guns, replacement parts just drop into place without any modification, but on many older guns, replacement parts need to be fitted before they will work correctly. Glock pistols, AR15 rifles, and Ruger 10/22 rifles are designs where most replacement parts fit right into place. And 1911 pistols are an example of an older design where replacement parts need to be fitted before they will work correctly.
Double action revolvers are an older design, and they are really hand fitted guns. This means that if you damage a part, and then you buy a replacement part, it may still take significant skill and knowledge to fit the new part correctly. That does not mean that you should be afraid to work on these guns, but using appropriate caution when modifying parts can save a lot of hassles.
It is also worth noting that modern manufacturing techniques have made the fit of parts in current Smith & Wesson revolvers much more consistent than it was in years past. And some parts that have historically required fitting are likely to drop into place on current production guns. But even with improved consistency, revolvers are still hand fit guns, and you have to be prepared for some parts to require fitting.
1.5 Required tools
When someone asks me about working on revolvers, I tell him that he should start by budgeting about $100 for a set of gunsmith screwdrivers. I say that mostly to make a point. If he thinks investing in tools is ridiculous, then I tell him to leave working on revolvers to the professionals.
You do not necessarily need to spend $100 on screwdrivers, but you will need quality gunsmithing screwdrivers, and you will likely need some other tools as well. In fact, if you plan to work on more than one gun, you should consider getting a full set of gunsmith screwdrivers that really will cost almost $100.
Gunsmithing screwdrivers are different than hardware store screwdrivers, and using the wrong screwdrivers will give poor results. The slots in hardware store screws are made in a few standard sizes, and they accept wedge shaped screwdrivers. The slots in gun screws are much more varied, and they are designed for hollow ground screwdrivers. You must use hollow ground screwdrivers that fit the screws very well, or you will damage the screw heads.
If you want to do trigger work, you will also need a trigger scale. It is not possible to accurately judge the pull weight of a trigger just by feel. So if you make changes to a trigger, you will need a trigger scale to understand the results of the change.
In fact, if you are working with double action revolvers, you may need two trigger scales, one for heavy triggers, and one for light triggers. Many trigger scales have a max weight of 12 lb, and 12 lb is sometimes not quite enough to measure the double action on revolvers with stock springs. So you may want a scale with a higher weight limit for some double actions. But for working with the single action, you need precise accuracy for light triggers in the 3lb range. If you need to pick out one trigger scale, I recommend choosing one that is accurate at the low end and goes up to 12 pounds, but be aware that it may not work in every situation.
1.6 Removing the sideplate
When people try to change springs in a revolver, they often have problems before they have even gotten to the springs. Before you can do any work on a Smith & Wesson revolver, you need to know how to remove the sideplate without doing cosmetic damage. Start by taking a minute to examine the screw heads, and also examine the lines where the sideplate meets the frame. On S&W revolvers, the line where the sideplate meets the frame is very fine.
The two main tricks to removing the sideplate without damage are: use perfect fitting screwdrivers, and never pry on the sideplate. It is also important to keep track of the screws and put them back in their original locations. The screws can be different in small but important ways.
After removing the screws, you remove the sideplate by tapping on the grip frame with a piece of wood or plastic. The vibration from tapping will make the sideplate loosen and rise up. Both of the videos mentioned earlier include good demonstrations of removing the sideplate. After the sideplate is removed, pay special attention to the edges of the sideplate and the frame. If you get any dings in the edge of either part, those marks will be quite visible when the gun is assembled. When I remove a sideplate, I put it in a ziplock bag so that it will not come in contact with any other metal parts.
Of course, minor cosmetic damage will not affect how a gun shoots, but it will have an effect on the value. People who know guns pay attention to the screw heads on a used gun, and they will significantly devalue a gun if the screw heads are damaged. This is especially true for Smith & Wesson revolvers. Damaged screw heads indicate that a gun was opened by someone without proper training. And the damaged screws always raise the question: "What did this person do after they got the gun open?"
You should also be aware that it is not necessarily easy to replace the screws if they get damaged. On a blued gun, replacement screws may not exactly match the bluing. And on older guns, the screw which retains the yoke and the cylinder is a fitted part. This screw is called the yoke screw, and it needs to be fitted so that it will securely retain the cylinder, but will not bind when the cylinder is opened. So if you had to replace the yoke screw, the new one might need fitting before it would work correctly.
Overall, it is not difficult remove the sideplate without leaving a single scratch. But you do need proper tools and proper procedures to get good results.
2 Part Two: Working with Springs
Part two covers more detailed information about revolver springs, polishing action parts, and how to test the results of your work.
2.1 Two important springs
There are two springs which control the trigger in a Smith & Wesson revolver: the mainspring and the rebound spring. The mainspring, sometimes called the hammer spring, is the spring which drives the hammer forward to fire a round. The rebound spring, sometimes called the trigger return spring, is the spring which returns the trigger to its forward position after a shot is fired. These springs work together to create a reliable and safe handgun. And these springs, along with the shape and condition of the internal parts, determine the feel of the trigger pull.
The mainspring's job is to drive the hammer forward with enough force to reliably ignite primers. By far, the most common cause of misfires is a weak mainspring. The rebound spring's primary job is to reset the trigger after each shot. But the rebound spring also performs other important functions. It has a critical role in single action function, and it also has a role in the internal safety functions of the revolver. So the interaction between these springs can be complex and subtle.
The next sections will discuss more details about how these springs behave.
2.1.1 Single action pull weight
The weight of the single action trigger is determined by two factors: the shape of the engagement surfaces on the hammer and trigger, and the strength of the springs.
The single action engagement points on the hammer and trigger wear quite well, so most of the time you will find them in good condition. But if you do have problems with the single action, you can find more information in the section on single action safety issues and in the appendix sections on push-off and working on the single action.
If the engagement surfaces are in good condition, then the weight of the single action trigger is largely determined by the strength of the rebound spring. When you cock a revolver, the rebound spring keeps the trigger pressed against the hammer so that the gun will stay cocked. So the rebound spring does the job that the sear spring does in a semi-auto pistol. And because it acts as the single action sear spring, the rebound spring has a large effect on the weight of the single action.
The mainspring only has a minor effect on the single action trigger weight. In some cases, changing to a lighter mainspring does not even have a measurable effect on the single action trigger. If your only goal is to lower the weight of the single action, then just switching to a lighter rebound spring often works well. This is a case where just changing a single spring often gives good results. However, if you change the rebound spring, you do need to check the trigger return and make sure it is still reliable. In some cases, you may have to do some polishing to get a good trigger return with a lighter rebound spring.
2.1.2 Double action pull weight
The double action trigger weight is affected by many more components than the single action. When you pull the trigger for double action, your finger has to overcome both the mainspring and the rebound spring. The mainspring is strong, and it has a large effect on the double action weight. The rebound spring also contributes to the double action weight, but it has a less significant effect than the mainspring. Any rough surfaces or friction also affect the double action trigger, and in some cases this friction can be very significant.
To significantly lighten the double action trigger, you need to lighten the mainspring. But when you work with the mainspring, you need to be very careful not to compromise reliable ignition. Lightening the rebound spring can also reduce the double action pull, but the effects of the rebound spring are less significant.
2.1.3 Drop safety and balancing the springs
If you are working with lighter springs, you need to understand the balance between the springs. And to understand that balance, you need to be familiar with the safety features in Smith & Wesson revolver. You probably know that a revolver has no external safeties, but a revolver does have internal safety mechanisms. These internal safeties insure that the revolver cannot fire if it is dropped, and drop safety is very important. No handgun should be carried unless it is drop safe.
The basic principle of drop safety in a Smith & Wesson revolver is that the hammer cannot strike fully forward unless the trigger is held to the rear. If you dry fire a Smith & Wesson revolver, and then hold the trigger back after firing, you will see that the hammer comes fully forward, and the firing pin protrudes through the breech face. Now, if you slowly release the trigger, you will see that as the trigger comes forward, the hammer moves back about an eighth of an inch. After the hammer moves back, the firing pin no longer extends through the breech face. What happens is that a raised area on the rebound slide engages with the bottom of the hammer and pushes the hammer back. And once the hammer moves back, it is blocked from moving forward again until the trigger is pulled. So the firing pin can only come in contact with a primer if the trigger is pulled. The interaction between the hammer and the rebound slide is demonstrated in this video: MidwayUSA - Safety Features of the S&W Revolver.
This interaction between the rebound slide and the hammer helps make the revolver drop safe, but it also requires a balance between the mainspring and the rebound spring. When the rebound spring pushes the trigger forward, the rebound spring must overcome the mainspring sufficiently to move the hammer backwards. So you cannot use a very light rebound spring unless you also lighten the mainspring.
The mainspring and the rebound spring also need to be balanced for the trigger to have a good feel. If the rebound spring is too weak, then the trigger return will feel sluggish. This sluggish feeling makes it impossible to shoot double action rapidly. In extreme cases, the trigger may not reset at all, which can make the gun lock up until the trigger is pushed fully forward. With correctly balanced springs, the trigger return on a Smith & Wesson revolver is very quick, and it is not possible to outrun the trigger with your finger.
In addition to spring strength, the trigger return can be very affected by friction and rough parts. Of course, rough parts never make the trigger feel good, but the trigger return is the most likely place to have real problems due to friction. If a lighter rebound spring makes the trigger return inconsistent or very sluggish, then the action likely needs polishing. And on many revolvers, polishing is necessary to get a properly balanced feel with a lighter springs. There is more information about polishing in the section on polishing internal parts.
18.104.22.168 Hammer block safety
Smith & Wesson revolvers with exposed hammers have another drop safety mechanism called the "hammer block" safety. Some people say that the hammer block should be removed because it is unnecessary and causes problems with the trigger pull. This view is wrong on all counts. If the hammer block is removed, the revolver is not drop safe and should not be carried. The modern version of the hammer block safety was developed after an accident during World War II where a Navy sailor was killed by a dropped revolver. And it was considered important enough that the hammer block was retro-fitted into revolvers that were already in service at the time.
More importantly, there is no reason to remove the hammer block. When the hammer block is fitted properly, it moves freely and has no effect on the trigger pull. And if the hammer block does cause friction, that can easily be fixed by careful stoning.
The hammer block is demonstrated in this video: MidwayUSA - Safety Features of the S&W Revolver.
2.2 Understanding spring strength and light strikes
When we talk about installing lighter springs in revolvers, there is an implication that the original factory springs are stronger than necessary. This implication is partly true, but the reasons for the strength of the factory springs are worth discussing.
2.2.1 Strong factory springs
The factory springs are designed to be more than strong enough in all possible situations. For example, strong springs help with reliability when guns are poorly maintained. If dirt gets in the action, if no lubrication is used, or if lubricants become congealed in freezing conditions, then extra strong springs can help the gun function. The factory springs have an extra margin of strength to overcome these adverse situations.
There are also many parts of a revolver which are supposed to fit with tight tolerances. If any of these areas are out of specification, it can cause light primer strikes and misfires. An extra strong mainspring can still be reliable even if some things are out of spec. But to get reliable strikes with a lighter mainspring, the gun must be in good condition and well maintained. There is more information about the important specifications in the section below on issues which cause light strikes.
2.2.2 Double action has a weaker hammer fall
One important consideration about spring strength is that the hammer does not strike as hard in double action as it does in single action. When a revolver is fired double action, the hammer does not come back as far as it does when the revolver is cocked for single action. This difference in the length of hammer the fall has a significant effect on the strength of the hammer strike.
If you need a revolver to be reliable in double action, then you must test it in double action. This issue is very important. I have seen people who primarily shoot single action be very surprised to discover that their guns had misfires in double action. This happened with guns that were 100% reliable in single action.
You can find more information about testing revolvers for reliability in the section on testing spring changes.
2.2.3 Issues which cause light strikes
The number one cause of light strikes and misfires is a weak hammer strike. This point cannot be overstated. Most of the time when people have misfires, it is because the mainspring tension is insufficient, and the hammer is not hitting hard enough. Low mainspring tension may be caused by either a weak mainspring, or by a loose or improperly fitted strain screw. You can find more information about mainspring tension in the section on working with mainsprings and the strain screw.
However, there are also mechanical problems which can contribute to light strikes. If these mechanical issues are just slightly out of spec, the revolver will often work reliably with a strong mainspring. But if tolerances are too far off, then you may get misfires even with a very strong spring.
The descriptions below illustrate some of the mechanical issues which can cause light primer strikes. A complete description of how to check all of these areas is beyond the scope of this article. But you should be aware that a qualified gunsmith will check most of these areas while doing a trigger job, and most of these tolerances can be checked quite quickly. You can find more information about these issues in the references section of this article.
- Firing pin length and protrusion
- You may get light strikes if the firing pin does not protrude far enough through the breech face. On guns which have a frame mounted firing pin, the overall length of the firing pin also needs to be sufficient. There is more information about firing pins in the appendix.
- Endshake is the amount that the cylinder can move forward and backward. If there is too much endshake, then the cylinder can move forward when the firing pin strikes the cartridge. This movement can use up energy that should have been delivered to the primer.
- Headspace is the distance between the back of the cylinder and the breech face. If there is too much headspace, then the cartridges may be too far from the firing pin. On Smith & Wesson revolvers, the headspace is also called the "rear gauge."
- Friction and interference
- Excessive friction on the hammer or the firing pin can reduce the energy of the firing pin strike. Interference between the hammer and the edge of the frame can also drain power from the hammer.
- Off center strikes
- Primers are most sensitive in the center of the primer. If the firing pin strikes are off center, then a very strong strike may be required to get reliable ignition.
2.3 Springs for duty guns
The question of what springs are best for duty guns is a controversial issue, and before I discuss the choices about springs, I want to talk a bit about controversy.
There are some areas where experts have differing opinions. In some cases, people with decades of experience can be found on each side of an issue. And even though I cannot say which group is "right," you may still benefit from knowing about both sides. Knowing about the issue can help you form your own opinions, and it can also help you avoid accidentally stumbling into arguments.
Choosing springs for duty guns is one of these controversial issues. Earlier, we discussed some of the reasons why the factory springs are quite strong. But it is a controversial question whether the factory springs are "too" strong, or whether they are just right for a duty gun. Keep in mind that for a duty gun, reliability is the highest priority, and trigger feel is secondary.
There are three different opinions about what springs are best for duty guns.
- The factory springs should be left alone. Only deburring parts and careful polishing should be used to improve the trigger.
- The rebound spring can be slightly reduced, but the mainspring must be left untouched to insure strong primer strikes.
- Both springs can be modestly reduced.
Note that I have never heard anyone say that the springs in a duty gun could be changed very drastically. So even though these opinions seem contradictory, there is actually broad agreement that you need to take a very conservative approach to the springs in a duty gun. But exactly how to do that is a point of contention.
I am not going to give a recommendation here, except to say that if you are going to work on duty guns, then you need to give careful consideration to the springs.
2.4 Polishing internal parts
As we have already discussed, polishing and smoothing the action is an important part of getting a good double action trigger. Most revolvers need more than just lighter springs for the double action to have a good feel. And polishing is especially important for getting a brisk and consistent trigger return with a light rebound spring.
If you are patient and careful, you can learn to do basic action polishing. In many cases, just stoning the rebound slide makes a noticeable improvement. But you can also learn to identify and improve many other points of friction.
2.4.1 Jerry Miculek's trigger job video
If you want to learn about smoothing the action on Smith & Wesson revolvers, I recommend Jerry Miculek's Trigger Job video. I have no affiliation with this video, but I like it, and I am going to take a minute to discuss it. The video is available from MidwayUSA at the link below, and it is also available from other vendors if you prefer.
I recommend this video if you want to work on revolvers, whether you plan to polish parts or not. It provides a detailed introduction to how revolvers work, and Jerry is a clear and knowledgeable presenter. The quality of the close up shots on the internal parts is not perfect, but it is quite good. And the overall presentation is understandable for someone who is just getting started.
If you do want to smooth the double action trigger pull, this video gives a detailed introduction on how to do it. The video shows how to use a stone, which parts to stone, and very importantly, it also shows which areas not to touch. Knowing what not to touch is a very important part of working on revolvers. Jerry also talks about the importance of a smooth trigger return, and he shows specific areas to polish which improve the trigger return.
Jerry does most of his work in the video with a Norton India stone. These are good quality stones that are very reasonably priced, but for some jobs I also like to use Brownell's white ceramic stones. Ceramic stones are more expensive, but they give a very fine finish. They can be used dry and then cleaned up with soap and water. And if you are careful with them them, they last a long time. Ceramic stones are not required, but you may find them useful.
I also want to emphasize one thing which is not shown in the video. No power tools are used in the video. All the work is done by hand with stones and files. I cannot emphasize enough that Dremel tools should rarely be used on guns. I have heard people say that for anyone who owns a gun, there should be a ten day waiting period to buy a dremel tool. I agree with this statement.
2.4.2 Dry firing to polish the action
Many people say that the best way to smooth a revolver action is to dry fire it a lot. While repeated dry fire will eventually smooth the action, I don't believe that dry fire is an efficient or effective method of polishing.
Dry firing does not smooth out imperfections as well as stoning the parts by hand. For example, consider the pin which runs through the top of the rebound slide to guide the hammer block safety. It is fairly common for this pin to stick out slightly on the back of the rebound slide. So the end of the pin makes a bump on the back of the rebound slide where the rebound slide should be flat. And that "flat" back of the rebound slide rides against a flat area of the frame. If you polish the gun by dry firing, then the bump slowly wears down, but it also wears a groove in the frame. Eventually, the parts mate well together, but neither of them ever becomes flat. If you stone the rebound slide on a flat stone, and also gently stone the frame, then you can insure that both parts are flat and true. So careful stoning makes the parts better, and it does it quite quickly.
However, after you smooth the parts by hand, they will still improve a little more through use. So a moderate amount of dry firing is reasonable after you have polished all of the obvious rough spots. Or you can skip the dry fire and let the gun continue to break in through normal use.
2.5 J-frames vs larger frames
All Smith & Wesson revolvers have very similar actions. But there are some important differences between J-frames, which are the smallest guns, and the larger framed revolvers, which are the K, L, N and X frames.
The most visible difference is that J-frame revolvers use a coil mainspring, while all other S&W revolvers use a flat leaf mainspring. There are two important differences between a coil mainspring and a leaf mainspring: the tension of a coil mainspring is not adjustable, and the coil mainspring can be a source of friction.
The fact that coil mainsprings are not adjustable has both advantages and disadvantages. Because there are no adjustments, a coil mainspring is very straightforward to install. It either works or it doesn't, but either way there is nothing to mess with. The adjustable tension offered by a leaf mainspring is sometimes an advantage, but it can also be a source of frustration for new gunsmiths. The next section of this article discusses how to work with leaf mainsprings.
A disadvantage of coil mainsprings is that the spring can be a source of friction. As the mainspring compresses, it rubs hard against the strut that runs through the center of it. The correct name for that strut is the "mainspring stirrup." And the mainspring stirrup should be well polished if you want to have a smooth double action.
Another important difference between J-frames and the larger frames is the overall size and geometry of the guns. The geometry of J-frames does not allow them to have as good a trigger as the larger revolvers. And the mainspring on a J-frame cannot be lightened very much without compromising reliability. A J-frame revolver can still be improved by careful polishing and judicious replacement of the springs, but the double action on a J-frame will not equal the trigger on a well tuned larger frame revolver.
2.6 Working with leaf mainsprings and the strain screw
The leaf mainspring used in larger framed S&W revolvers is a very good system. Unlike a coil mainspring, a leaf mainspring does not touch anything as it is compressed, so there there is no unnecessary friction. Also, the tension on a leaf mainspring is set by a strain screw at the front of the grip frame, so the tension can be adjusted without any need to modify or replace the spring.
However, when people change springs for the first time, the leaf mainspring is often a source of frustration. I often hear complaints from people who installed a new spring and got misfires. And occasionally when someone installs a new spring, they find that the trigger pull has gotten much heavier. Both of these problems are caused by the incorrect assumption that a mainspring is a drop in part. Actually, to be precisely accurate, the mainspring is a drop in part, but the strain screw has to be fitted so that it puts the correct tension on the mainspring.
Most of the tutorials I have seen about changing springs don't mention that the strain screw will need fitting. But the spring vendors do state that "gunsmith installation is recommended," so they have actually given fair warning that anyone installing springs should at least be familiar with everything in this article. It's not their fault if those warnings are universally dismissed as useless boilerplate.
The strain screw appears simple, but there is actually quite a bit to know about using the screw to set mainspring tension. The first and most important point is that on any gun where reliability is critical, the strain screw must be firmly tightened down. Simply backing out the strain screw is not a way to make adjustments. If the strain screw is loose, it has the potential to back out further and cause misfires.
Also, there are limits to how much you can reduce the tension by shortening the strain screw. If the screw is too short, then the rebound slide can hit the mainspring when the rebound slide is at its rearmost position. Also, as the screw is shortened the spring gets straighter, and the geometry of the spring in relation to the hammer changes. This geometry can result in a poor trigger pull if the strain screw is too short. So even though you can reduce tension by shortening the strain screw, you still cannot get a very light trigger pull using the factory spring, and you may prefer an aftermarket reduced power spring.
However, with reduced power springs, a different set of problems can occur. Many people who install a reduced power spring immediately get light strikes and misfires. Often they conclude that the spring is not properly made or does not fit their gun, but most likely they just need a longer strain screw. Of course, this situation requires getting a new screw, which is not always convenient. But once you get a longer screw, things often work quite well. Using a longer screw generally does not cause problems, so a lighter spring with a longer screw can be a good way to get mainspring tension where you want it.
Another issue with fitting the strain screw is that many of the popular aftermarket springs have a groove in them. These springs are made by Wolff Gunsprings Company, and they have a ridge down the back of the spring and a corresponding groove in the front of the spring. If the tip of the strain screw fits into the groove, it effectively makes the screw shorter and makes the spring tension too light. Whether this issue happens depends on the exact shape of the tip of the strain screw, so you should pay close attention to this area. Some people do not like Wolff mainsprings because of the groove and also because they make a particular pinging sound when the hammer drops, but I have been very satisfied with the overall quality of Wolff springs and believe they are a fine choice.
You should also be aware that the factory strain screws on stainless steel guns are quite soft. Removing and reinstalling the screws multiple times can deform the tips and shorten the screws. This effect can also change how the screw fits into the groove in a Wolff spring. The blued screws are more durable, but it still never hurts to have a spare if you will be working with these screws frequently.
2.6.1 Shims and alternative strain screws
If you need a longer strain screw, and you do not have one available, there are some possible alternatives. You can add a shim to the end of the screw, or you can replace the strain screw with a different type of screw.
If you want to add a shim to the end of the strain screw, then a spent primer is an ideal material. Take a used small primer and clean out the inside of it. Then fit the primer cup over the end of the strain screw. I would not recommend this method for a duty gun, but if necessary, it can be an effective field repair. You can also add a large primer over the small primer if you need an even thicker shim.
For guns that will only be used for recreational purposes, you might choose to replace the factory strain screw with a socket set screw. The strain screws use a standard 8x32 thread, so a standard socket set screw will fit. Some people have reported good results using a socket set screw with Loctite to keep it from moving. I have used a socket set screw with blue Loctite, and it held fine. But on a duty gun, I would require a proper strain screw which could be tightened fully.
Note that while the strain screw uses a standard thread, the head is an unusual shape. So you will not find any screws at the hardware store where the screw head fits in the frame recess for the strain screw. The headless set screws are the only hardware store screws that will fit.
On a side note, if you use Loctite, I recommend keeping red Loctite away from guns. Red Locktite requires heat to break the bond, and it and should only be used in very specialized circumstances.
2.7 Single action safety issues: light triggers and push off
If you are working with light springs, there are two safety issues related to single action that you should be aware of: light triggers and push off.
The first concern is that the single action trigger pull should not be too light. The Smith & Wesson armorer's manual says the minimum weight for the single action trigger pull is 3 lb. Some people feel that 2.5 lb is acceptable, but there is debate about that point.
The problem with a light single action trigger is many people cannot safely control a trigger that is much below 3 lb. Even a 3 lb trigger can be very light if you are under stress or wearing gloves.
If you use light springs, and particularly if the rebound spring is light, then the single action trigger can end up very light. So if you make spring changes, you should check the weight of the single action trigger pull.
The other safety issue you should be aware of is push-off. Push-off is a condition where the hammer does not hold firmly when it is cocked, so if the cocked hammer is pushed forward with moderate pressure, it will drop. When testing for push-off, only moderate thumb pressure should be used. It is not necessary to use excessive pressure which could damage the parts.
Push-off is a serious safety condition. If the hammer can push-off, then the hammer could drop without the trigger being touched. The hammer block safety will usually prevent the revolver from firing if the hammer falls from push off. But that does not mean that push off is acceptable. If the hammer can fall without the trigger being pulled, then the action is defective.
A revolver with push-off should be examined by a qualified gunsmith. Sometimes push-off can be resolved by stoning the single action engagement point on the trigger, but in other cases, the hammer, the trigger, or both may need to be replaced.
Note that none of these safety issues with single action apply to revolvers which are double action only (DAO). Some people choose to resolve problems with the single action by modifying the hammer to make the revolver double action only. This modification can be done by grinding off the hammer spur, or by grinding the single action engagement notch on the hammer, or both. However, most people like the single action option and prefer to have the single action capability repaired.
2.8 Primer sensitivity
If you are working with springs in revolvers, you need to be aware that not all ammunition behaves the same. Some primers require a harder strike to set them off. The sensitivity of primers is often described using the terms "hard" and "soft," where hard primers require a stronger strike to ignite them.
Primer sensitivity can have an effect on many types of firearms, but it is especially important with double action revolvers. With most firearms there is no reason not to have a strong mainspring. For example, with semi-automatic handguns, the hammer is cocked by the movement of the slide. So it is not bothersome if the mainspring is quite strong. But with double action revolvers, your trigger finger needs to overcome the mainspring tension, so you want a mainspring which is strong enough, but not too strong. And you need to take primer sensitivity into account when you determine whether the mainspring is really strong enough.
Note that soft primers are not better than hard primers. All commonly available primers meet specifications used by the firearm industry. And a gun in that is in good condition should work with any commercial ammunition. If a gun works with some types of ammo and gets misfires with others, that is a problem with the gun, not the ammunition.
If you want more details about the sensitivity of specific types of primers, there is a section in the appendix.
2.8.1 Seating primers for competition revolvers
Soft primers have a special role in revolver competition. In some competitions, having the lightest double action is an advantage. And to have the lightest double action, you need to have a light mainspring without compromising reliability. So revolver competitors use Federal primers, which are the most sensitive, and they careful seat those primers below flush.
It is counter-intuitive, but deeply seated primers are actually more sensitive. People often think that deeply seated primers are farther from the firing pin and should be harder to set off, but this view is not correct.
If a primer is seated a bit high, then the primer can move deeper into the primer pocket when the firing pin strikes it. This movement absorbs some of the energy from the firing pin and can cause light strikes. Primers are most sensitive when they are seated right to the bottom of the primer pocket. And when primers are at the bottom of the primer pocket, they will be below flush with the back of the case.
Some competition revolvers use a mainspring so light that it is only reliable with deep seated Federal primers. But since these guns are only for competition, and their owners know exactly what to expect, the guns are entirely suitable for their intended purpose.
When you hear about revolvers with reliable 5.5 lb double action triggers, they are probably using only deep seated Federal primers. You can have a good trigger that is reliable with all types of ammunition, but it will be significantly more than 5 lb.
2.9 Double action trigger weight
The weight of the double action trigger pull can be used to make very general estimates about whether the mainspring tension is heavy enough. Of course, friction and the rebound spring also affect the double action trigger, so the pull weight does not give an exact measurement of mainspring strength, but it can still give a useful approximation. There is a more exact method for measuring mainspring strength described in the appendix.
The list below give some very general guidelines. Note that in this list "large frame" means any revolver except a J-frame.
- If the trigger pull is over 10 lb on a large frame or 11 lb on a J-frame, it should ignite all primers.
- Many large frame guns are fully reliable with the trigger at 9 lb or less. And many J-frames work fine at 10 lb or less.
- Large frame guns below 7 lb are generally competition guns that require specific primers.
Even though the trigger weights listed above leave wide gaps, they can still be useful for diagnosing problems. For example, if you have to increase the trigger pull well above 10 lb on a K-frame to get reliable ignition, then there is likely to be some mechanical issue besides the mainspring strength. And if a gun with a 7 lb trigger seems to be totally reliable with all ammunition, you should try testing with a wider variety of ammo before trusting it.
Some triggers will fall in between the listed weights, and you will need to consider those on a case by case basis. For example, a large frame revolver with an 8 lb trigger could be fully reliable if it is in excellent condition, but you would want to test it carefully. There is more detailed information about testing reliability in the section on testing spring changes.
2.10 Testing spring changes
If you change the springs in your revolver, then you need to test the gun to make sure it is still reliable. And when you plan your testing, you need to consider several factors. First, you should decide whether you need the revolver to be reliable with all ammunition, or whether it is a recreational gun that only needs to work with certain loads. And you should also keep in mind that the hammer does not strike as hard in double action.
If your goal is to have a gun that is reliable with all ammunition, then you should test it using hard primers. And if you are not certain which primers are hardest, then you should include a variety of ammunition in your testing. If you want more information about hard primers, there is a section in the appendix on the hardness of specific primers.
Also, if your revolver is a 357 magnum, you should include 357 magnum rounds in your testing. Some 357 magnum rounds use magnum primers, and these primers can be harder than the primers used in 38 special rounds. So a revolver that is reliable with commercial 38 special rounds may still have misfires with 357 magnum rounds.
And of course, you need to fire double action during testing. If you get reliable ignition with single action, that only proves that the gun will be reliable in single action.
Another important question is the number of rounds to use during testing. If the mainspring tension is borderline, it can result in misfires that only happen occasionally. So I recommend using a minimum of 50 rounds for testing. And using more rounds during testing is even better. Keep in mind that "testing ammunition" is really another name for training, so doing lots of testing can have an upside.
2.10.1 Adjusting the strain screw during testing
Even if you get 100% ignition during testing, that does not tell you whether your mainspring tension is just barely strong enough, or whether it has a wide margin of extra strength. If you have a leaf mainspring, then you can make adjustments to the strain screw to test how much tension is required.
For example, you can back out the strain screw until you get misfires, and then turn the screw back in a quarter or a half turn to ensure that you have enough tension. By testing in this way, you can insure that you are not too close to the point where you would get misfires.
Note that after you complete your testing, you should not leave the screw backed out. If backing out the screw gives you the amount of tension you want, then you should shorten the screw. If you need to shorten the screw, there are several ways to determine how much to shorten it. But keep in mind that the screw length is quite sensitive, and even a few thousands difference in screw length has an effect on the spring tension.
One method for determining how much to shorten the screw is to count the number of turns it takes to tighten it. For example, if you have backed out the screw to get the tension you want, then you can count exactly how many revolutions it takes to fully tighten the screw. Since the screw has 32 threads per inch, each revolution moves the screw tip .031". So if it takes 1.5 turns to fully tighten the screw, then you want to cut about .046 off the screw. However, I would recommend cutting a bit less than that and then testing the fit.
Another method to take measurements for shortening the screw is shown in Jerry Miculek's video in the videos section. Jerry uses a caliper to measure how far the head of the strain screw moves when he tightens it. This method is demonstrated starting at 4:20 in the video.
2.10.2 Do not trust the indent in the primer
When people are testing mainspring strength, they often fire a few rounds, and then examine the spent brass to see the depth of the firing pin strike. But the spent brass doesn't really give a true indication of the firing pin strike. If the round goes off, then the primer indent always looks good.
To understand why the primer indent always looks good, we need to consider the entire process that takes place when a round is fired. When you load a round into the chamber, there is always a gap between the base of the cartridge and the breech face of the gun. This gap is the headspace, and it allows room for the action to function. When the gun is fired, the firing pin protrudes through the breech face and extends through the gap to strike the primer. Then the primer ignites, and in turn ignites the main charge of propellant. When the propellant ignites, it generates a large amount of pressure to push the bullet down the barrel. But that same amount of pressure also pushes the brass case against the breech face. So when you look at spent brass, the primer indent looks the way it would look if there were no gap between the cartridge and the breech face. Even on guns where the firing pin retracts after it strikes, this effect still happens. The fired case presses back against the breech face faster than the firing pin can retract.
So when you look at spent brass, the primer indents are misleading. You only see what the firing pin indent really looks like when you look at a round that misfired. And if you do get misfires, you may be surprised how small the primer indents are.
The appendix covers reference material and extra information that may be useful for specific projects. The answers to many common questions about revolvers will be found in this section.
3.1 Reference materials
If want to work on revolvers, there are a number of reference materials you should be aware of.
3.1.1 Online forums
There are two online forums devoted to Smith & Wesson firearms.
There are many extremely knowledgeable people who read these forums and who are willing to answer questions. However, before you post a question, you should search on the forums to see if your question has already been asked and answered.
3.1.2 Smith & Wesson revolvers FAQ
There is an excellent collection of frequently asked questions (FAQ) about Smith & Wesson revolvers that is available online. This FAQ is hosted at each of the Smith & Wesson online forums.
This FAQ is really a short reference book about Smith & Wesson revolvers. If you want to work on revolvers, this FAQ is invaluable.
3.1.3 Kuhnhausen's shop manual
Jerry Kuhnhausen is a gunsmith who is known for his detailed reference books about firearms. For many firearms, you will hear people say "If you want to work on that, you need Kuhnhausen's book." Smith & Wesson revolvers are no exception.
Here is a link to purchase the Smith & Wesson revolver manual from MidwayUSA. Of course, the book is also available from other vendors.
Note that Kuhnhausen's book is more of a reference book than a tutorial.
3.2 Rimfire vs centerfire
There are important differences between rimfire and centerfire ammunition. In general, it takes a harder hammer strike to ignite rimfire rounds than centerfire rounds. So rimfire revolvers need a stronger mainspring, and as a result they have heavier double action triggers.
For revolvers with a leaf mainspring, the same mainspring is used for rimfires and for centerfires, but rimfires may use a longer strain screw to set the tension higher. For J-frame revolvers, the rimfire models use a stronger mainspring. Because of the heavy mainspring and smaller geometry, J-frame rimfire revolvers will not have very good double action triggers. You can still make improvements to the double action on a rimfire J-frame, but it will never equal the trigger on a well tuned centerfire K-frame.
Rimfire and centerfire rounds also respond differently if the hammer is lightened. This issue is discussed further in the next section.
3.3 Despurred and lightened hammers
Some factory double action only (DAO) revolvers have hammers which do not have a thumb spur for cocking. These hammers are called spurless hammers or bobbed hammers. Some people prefer a spurless hammer since it cannot catch on clothing during the draw.
People who prefer a spurless hammer often ask "If I make the hammer lighter by cutting off the spur, will I need a stronger mainspring?" For centerfire revolvers, the short answer to this question is "no." But the reasons why require a longer answer.
As an aside, if you want to bob a hammer, I recommend saving the original hammer and buying a new hammer to cut down. The new hammer may require fitting, but if you get a new hammer, then the change is reversible. If you modify the original hammer, it may be difficult to put the gun back to original condition if you ever change your mind.
Now before we discuss why lighter hammers work fine with centerfire rounds, lets talk some more about differences between rimfire and centerfire. For rimfire rounds to ignite, the rim of the round needs to be crushed. As discussed in the previous section, it takes fairly strong mainspring to crush the rim, and it also requires a heavy hammer. So you should not try to bob or lighten the hammer on a rimfire revolver.
Centerfire primers can be ignited by a high velocity strike, even if there is not a huge amount of mass behind the strike. And this is why light hammers work well with centerfire rounds. When you lighten the hammer, that does not change the amount of energy stored by the compressed mainspring. And when the same amount of energy is applied to a lighter hammer, the hammer achieves a greater velocity. Since energy equals mass times the velocity squared, a lighter hammer with greater velocity typically has more kinetic energy than a heavier hammer.
If you want more detailed explanations about the physics of hammer strikes, then google will give you lots of results. There have been many long and contentious debates on internet forums about the velocity, energy, and momentum of revolver hammers. But for most purposes, these explanations are not required.
The practical summary is that using a bobbed hammer on a centerfire revolver does not cause problems. There is actually an ideal weight for hammer efficiency, and if you go below that weight, you will not get a hard enough strike. But because hammers are primarily designed for manufacturing efficiency and appearance, most factory hammers are far above that ideal weight.
In fact, competition shooters have found that using a lighter hammer actually allows the use of a lighter mainspring without compromising ignition. So using a lighter hammer is a common part of tuning a competition revolver. When you hear about double action trigger pulls below six pounds, those guns usually have lightened hammers.
In the thread linked below, there is a picture of a very cut down hammer. The thread is mainly about push-off, and I have included another link to the same thread in the section about the causes of push-off. But the thread was started by gunsmith Mike Carmoney, and the photos at the beginning show one of his revolvers. Carmoney is well known for his work on lightened hammers. And if you look closely at the the photos, you can see how significantly the hammer has been cut down. And since it is one of Carmoney's guns, you can be sure that the hammer provides excellent performance.
There are differing opinions about what causes push-off and how to test for it. This section will discuss these questions. If you do have push-off, there is information about resolving it in the section on working on the single action.
3.4.1 Causes of push-off
People sometimes think that light springs cause push-off, but that is not quite true. Push-off is caused by incorrect shape of the single action engagement between the hammer and trigger. If the engagement surfaces are perfect, then the hammer will not push off even with very light springs. However, if the single action engagement is marginal, then light springs may make the condition apparent. So it sometimes appears as though light springs cause push-off, but the springs are really just revealing an existing issue.
The fact that springs do not cause push off is illustrated in the thread below from Brian Enos's forums. The thread was started by Mike Carmoney who is a retired revolversmith who is renowned for his competition revolvers. Sadly, the thread became contentious and had to be closed to new comments, but it still contains useful information.
3.4.2 Testing for push-off
There are differing views about how much pressure should be applied to the hammer to test for push off. But there is general agreement that the pressure should be moderate, and that excessive force should not be applied to the engagement surfaces. However, there is no exact agreement about what moderate means.
If you want to measure how much force you are using to test push off, you can do your testing on a scale. Start by holding the muzzle of the unloaded gun pointing downward on the scale. Then as you press on the cocked hammer, the movement of the scale tells how much pressure you are applying.
Here are the instructions from several high quality sources about how much pressure should be used to test push off.
The thread below from smith-wessonforum.com has an extensive discussion about push-off. Post #34 in this thread has an excerpt from the Smith & Wesson armorer's manual which specifies not to exceed 6 lb of pressure when testing push-off.
- In the 1990 edition of his book The S&W Revolvers: A Shop Manual, Jerry Kuhnhausen recommends using 16 lb of pressure to test push off. However, he also acknowledges that some other experts recommend only 10 lb or 12 lb.1
- However, in the expanded 5th edition of his S&W revolver shop manual, released in 2014, Jerry Kuhnhausen recommends using 12 lb of pressure to test push off.2
With sources like the S&W armorer's manual and Jerry Kuhnhausen, I cannot offer an opinion about which is best.
3.5 Working on the single action
On a Smith & Wesson revolver, the engagement points for the single action are a notch in the hammer and a small surface on the back of the trigger. For this discussion, we will call the single action surface on the trigger the "single action sear".
Most of the time there is no need to touch the engagement surfaces, but in some circumstances it may be necessary. The most common reason to touch the engagement surfaces is to fix push-off. There can also be cases where the single action is too heavy or too light after the springs have been set appropriately, so it is necessary to stone the single action sear to fix the pull weight.
If it is necessary to modify the single action engagement, I recommend that you take the work to an experienced gunsmith. It is possible to stone the single action sear on a bench with a 6" stone, but just because the tools are simple does not mean that the task is simple. Stoning the trigger incorrectly can destroy it. So if you do this work yourself, you should be prepared for the possibility of needing to replace parts.
However, whether or not you do the work yourself, you should still be familiar with what is involved. On a Smith & Wesson revolver, the single action notch in the hammer is only about .005" deep. This is less than one quarter of the engagement on most firearms. This small depth helps give an excellent trigger pull, but it also means that the surfaces need to be very precise.
Both the hammer and trigger are case hardened. This means that the interior of the parts are relatively soft steel, and only the outer surface is hardened. Typically, the case hardening is about .005 thick. Case hardened parts give a good balance of hardness and durability, because even with a very hard surface, the softer interior prevents the part from shattering. But you need to be careful not to cut through the hardened outer surface or the part can be ruined. The hammer notch and the single action sear need to be very hard or they will wear out quickly. So it is critical not to cut through the case hardening in these areas.
Due to the very small and precise shape of the hammer notch, it cannot be reshaped by stoning. In some cases, it is possible to stone out a very small burr or imperfection in the hammer notch, but if there is any significant damage, then the hammer has to be replaced. When it is necessary to work on the single action engagement, the modification is always done on the single action sear of the trigger.
To stone the single action sear, you must use some type of jig. The surface is very small, and the angle needs to be very carefully controlled. There is a well known method for stoning the single action sear where the trigger and a 6" stone are both held against a flat bench. This method is pictured in post #6 of the Smith & Wesson smithing FAQ. Even though this method seems "freehand," the stone and the bench actually form a precise and repeatable jig.
The single action sear can also be stoned using a specialized gunsmithing jig. The best known jig for this job is the "Power Custom - Series I Stoning Fixture" which is available here from Brownells. In addition to the jig, you need a Smith & Wesson revolver adapter and stones that fit the jig, so this setup is not economical for most home gunsmiths. Luckily, this jig rarely necessary when working on revolvers. But you should be aware that your gunsmith has a variety of tools and methods at his disposal, and he will determine the best method based on the job at hand.
But regardless of which jig or stones are used, the most important aspect of stoning the single action sear is to stone the least amount necessary. If you cut through the case hardening, the part is ruined. But with a cautious approach, problems with the single action can often be resolved without replacing parts.
3.6 Firing pins
A weak mainspring is the most common cause of misfires, but the second most common cause is a short firing pin. Over the years, Smith & Wesson revolvers have used two different types of firing pin. Earlier guns had the firing pin attached to the hammer, and then in the late 1990s, they changed to a system with the firing pin mounted on the frame.
The older style hammer mounted firing pin is correctly called a "hammer nose." And the hammer nose firing pins rarely have problems. The only thing that sometimes needs attention is the amount of protrusion through the breech face. Most sources say that the protrusion should be .050 - .060.
Some people recommend checking firing pin protrusion by holding a dime against the breech face next to the firing pin, and checking that the firing pin extends at least the thickness of the dime. This check is known as the "dime test." Since a US dime is about .052 thick, the dime test is a reasonable cursory check for firing pin protrusion.
More recently manufactured revolvers use a frame mounted firing pin (FMFP). The key factor with frame mounted firing pins is the overall length of the firing pin rather than the protrusion. The length is important because the firing pin needs to have sufficient protrusion in the front, but it also needs to extend far enough at the back for it to be firmly struck by the hammer.
The frame mounted firing pins have gotten a bad reputation for being unreliable, but the system actually works well if everything is within specifications. Unfortunately, some years ago Smith & Wesson made some firing pins that were too short. In many cases, the short firing pins were only reliable with a very strong mainspring, and in some cases, they were not reliable at all. These short firing pins earned a bad reputation for the frame mounted firing pin system, but really it was only the short firing pins that deserved the bad reputation.
Luckily, on guns with the frame mounted firing pin, the firing pin is easy to replace after you remove the sideplate. And Smith & Wesson corrected their firing pin design, so firing pins produced in the last several years work fine.
The preferred length for Smith & Wesson frame mounted firing pins is .495. If the pin is less than .492, you should replace it. Many of the problem pins were .485 or less, so the differences in length can be fairly significant. I have recently purchased factory replacement firing pins, and the ones I received are about .494 inches, which is acceptable.
3.6.1 Extra length firing pins
Several companies make extra length firing pins for revolvers that have frame mounted firing pins. Extra length firing pins may be useful in some specially tuned competition guns, but in most circumstances, the disadvantages outweigh the advantages.
People who have done testing with different length firing pins have reported differing results. Some people have found that longer firing pins do not perform better than a standard .495" firing pin. Others have found that extra length firing pins do give better ignition in lightly sprung competition guns. My recommendation is that if you get misfires with a stock .495 firing pin, then you should check the mainspring strength and look for other mechanical issues. Firing pin length is likely not the problem.
And long firing pins have a risk of puncturing primers. If the primer is punctured, then escaping high pressure gasses can cause erosion and damage to the firing pin and the firing pin bushing. In unlucky cases, the firing pin can get caught in the primer and jam the revolver so that the cylinder cannot rotate. So an extra length firing pin can have significant downsides.
Some extra length firing pins specify that you must use snap caps when dry firing. This requirement does not apply to all extra length firing pins, but if you choose an extra length pin, you should look closely at the instructions. If it says that you must use snap caps for dry firing, you should what it says. Failure to use snap caps when required can result in breaking the firing pin or overcompressing the firing pin spring. Of course, using snap caps is always a fine idea, but small amounts of dry fire will not harm a centerfire Smith & Wesson revolver with a stock firing pin.
So overall, extra length firing pins are not a good choice for duty guns, and they should be treated cautiously in guns for recreation.
3.7 Details on primer sensitivity
A comprehensive discussion about the sensitivity of different primers could fill its own article. This section will only provide a brief list of useful points. If you want more information about primer hardness, you should search on internet forums where revolvers or reloading are discussed. You will find lots of information, and you will also find that people have differing and strongly held opinions on this subject.
- Federal primers are the softest. This point especially applies to Federal pistol primers that are used for reloading, but commercial Federal ammunition also has soft primers. If a gun is reliable with Federal ammunition, that does not prove that it will be reliable with other brands.
- Many 357 magnum rounds use magnum primers instead of standard primers, and magnum primers are often harder than standard primers. So some 357 magnum rounds require a pretty strong mainspring.
- CCI primers used to be widely known as the hardest, but this is no longer the case. CCI changed the formula a few years ago, and their standard pistol primers are no longer especially hard. However, CCI magnum pistol primers are still fairly hard.
- As demonstrated by the previous point, comparisons of primer sensitivity are not guaranteed to stay the same over time. Manufacturing formulas can change. Also, some smaller ammunition manufacturers buy primers in bulk instead of manufacturing them, so the primers they use may vary according to market availability.
- Some people have reported that the primers used in Remington UMC ammunition are relatively hard. If you are testing reliability with a variety of ammunition, these might be a good one to include.
- Some non-toxic primers are quite hard.
3.8 Modifying springs
You will often hear the suggestion to lighten a spring by cutting a coil or two off of it. This practice was common when factory springs were the only ones available. But with the variety of springs currently on the market, cutting springs is not a preferred practice.
To understand why cutting springs is not ideal, you need to consider what happens when you cut a spring. When you shorten a spring, you are not actually making it lighter. In other words, the amount of pressure required to compress the spring a given distance is not reduced. Instead, when you shorten a spring, you are reducing the amount of pressure that is pre-loaded on the spring when it is installed. If you look at lighter weight aftermarket springs, they are usually at least as long as the original springs, but made of thinner wire. So the aftermarket springs are easier to compress due to the thinner wire, but the amount of pre-load is not necessarily reduced. Since the length and strength of reduced power springs was specifically designed for their intended use, they often give better feel and function than cut springs.
However, there may still be cases where you choose to modify coil springs. If you do cut springs, look closely at how the original ends of the spring are finished, and try to bend or grind the cut ends to look similar.
You may also hear about methods to modify flat leaf springs. Some people bend leaf springs, or grind them to make them thinner or narrower. I do not recommend modifying leaf springs. Some experts do get good results by modifying these springs, but it takes expertise to modify them without damaging them. Minor imperfections in leaf springs can become stress points and lead to breakage. Even very small scratches from grinding can drastically shorten the life of a flat spring.
3.9 Measuring mainspring strength
On revolvers with an exposed hammer, you can measure the mainspring tension with a trigger scale. To take this measurement, you start by dry firing the revolver and holding the trigger to the rear. Then with the trigger still held to the rear, you hook your trigger scale around the front of the hammer, and measure how much weight the hammer will hold before it starts to move. Note that it is important to keep the trigger held to the rear so that the trigger and the rebound spring will not be in contact with the hammer.
Post #2 in this thread has an illustration of how to take this measurement:
This method of measuring the mainspring tension is used by Smith & Wesson armorers, and there is a factory specification for the mainspring tension. For 38 special revolvers, the hammer should support 3.25 lb, and for 357 magnums, the hammer should support 3.5 lb.
For some newer guns with frame mounted firing pins, the shape of the hammer face is different from the older guns, so the factory specification weights above may not be accurate. But you can still use this method to compare the hammer tension between similar guns.