Do it Yourself Action Job

Before we start any gunsmithing, there are a few principles that we need to apply.

The first principle is similar to the doctor’s oath- do no harm. Don’t make a problem worse than it already is and don’t make new problems. If you are uncertain about what you are doing, consider having the work done by a professional. 

The next principle is to be certain what the problem is. An incorrect diagnosis (again with the doctors) will waste time and effort and may cause more serious problems (back to principle one). Quite often I read someone’s description of a problem and immediately consider more than one possible cause. A series of questions or an examination of the weapon is necessary to determine the exact cause. Meanwhile, several well-meaning individuals will respond with fixes for the most common cause or the problem they have personally experienced; whether these fixes are correct or not. Beware someone who states with absolute authority what the problem is without ever examining the weapon.

The third principle is to use the correct tools. It’s almost always cheaper to buy, borrow or rent the correct tool than to have to replace a piece damaged with an incorrect or jury-rigged tool.  Gunsmithing screwdrivers are different from standard, household screwdrivers. If you don’t know how to grind your own screwdrivers, invest in a good set.

An addendum to this third principle would be to know how to use the tools correctly.

The fourth principle is to try to work on the least expensive part. It’s cheaper to start filing on a front sight housing and wreck it than it is to start filing on the barrel and wreck that. Sometimes it’s not possible to correct the problem without modification or replacement of a major component. Remember that any work you do will probably void the warranty. Make certain that you don’t want to try to get repairs done under warranty before you begin work. Most manufacturers will warranty incorrectly manufactured parts as long as they’re still in business.

Working on the least expensive part may mean expense in terms of time rather than money. Let’s say you have a problem with two possible causes. The first is the most probable but will involve major machine work to correct. The second is much less likely but will be a quick and easy fix. Despite the lower probability, it would be advisable to try the quick-fix first rather than spend the time and effort on the major fix only to find out it wasn’t the problem. Otherwise, it’s generally best to start with the most likely problem and work your way down

Fifth, don’t use force. If force is necessary, make sure you apply it correctly

There are three factors that determine how well an action works; they are friction, spring tension, and geometry. Action jobs entail modifying one or more of these factors to suit the end user.  

Friction simply means how easily parts move against one another. Friction can be reduced by polishing, plating, lubricating or cleaning parts. Friction can also be increased. Reducing friction reduces wear between parts. Changes in spring tension or geometry can affect friction.  Quite often a customer would come into the shop looking for an action job when all they needed was a cleaning, inspection and reasonable lubrication job.  It is difficult to absolutely control the amount of lube inside the mechanism. Make sure any work you do is not critically dependent on running either lube-free or heavily lubricated. You may have a marvelous trigger when the mechanism is dry that becomes unsafe if any lubrication gets on it.  

Spring tension means how much pressure is exerted against the mechanism by the various springs. Spring tension can be changed by replacing springs, modifying springs, or using adjustments built into the mechanism. Adjustment mechanisms can also be added. Changes in geometry may affect spring tension.

Springs perform a function- most often a necessary function. By reducing the tension on a spring you are reducing its ability to perform its function. An example is the trigger return spring. One way to reduce felt trigger pull is to reduce the trigger return spring tension. If taken too far, the trigger return can become sluggish or the trigger may fail to return at all. Likewise, if a mainspring is lightened too much it may not exert enough force to reliably ignite primers. Lighter trigger return or main springs may be acceptable in a target arm where they wouldn’t be in a self-defense weapon.

Physically modifying a spring to lighten it may also damage it and lead to premature failure. Replacing a spring with a lighter tension, properly designed, quality spring is generally preferable to modifying an existing spring. Coil springs often have finished ends and clipping coils can lead to accelerated wear on the parts in contact with the clipped end or the clipped end my no longer fit the associated parts. Grinding a leaf spring can ruin the temper or create a weak spot. Stretching a spring beyond its design limits can damage the spring.  

Geometry means how the various parts interact with each other. Changing the shape or relative position of the parts will affect how they move and how the mechanism overall functions. The mechanism is a system and changing a single part can affect all the other parts plus relatively small changes can lead to large effects.  

When modifying two associated parts it may be acceptable to change one of the parts where changes in the other part would cause problems. Sometimes the overall interaction of the parts is not obvious which is where factory training can come in handy. Often, changing the geometry means returning the system to its original design specifications. Wear, damage, or mis-fitted factory parts can cause a mechanism to be out of spec.  

Shims, bushings or oversized pins can all be used to limit unwanted movement of parts. When the parts move more consistently in relation to each other it’s easier to get everything working properly and will reduce wear in the system. Sometimes it may be necessary to replace an existing part with an oversized part that is then fitted to the weapon.  

A typical application of geometry is in sear adjustment. The sear is similar to a ball sitting on a shelf. To fire the weapon you want to push the ball until it falls off the edge of the shelf. Two ways you can change the geometry are engagement depth and engagement angle. By changing depth you shorten the distance you have to push the ball before it falls. You can shorten the distance by shortening the shelf or by putting something behind the ball to hold it closer to the edge. If you shorten the distance too much, the ball will fall every time a truck passes by. 

To change the engagement angle, you tip the shelf forward or back. If the shelf is tipped back, you have to push the ball uphill to get it to drop and it takes more effort. If the shelf is tipped forward, the ball will roll off all by itself.  

As the parts wear, both engagement depth and engagement angle may change over time. Try to allow for wear.

When removing material always remember that it’s much easier to remove material than it is to add material (if not downright impossible). Always work slowly and make sure you’re only removing material on the surfaces you want to reduce and be careful to maintain angles. Using an abrasive that’s finer than you need is better than using one that’s too coarse even though it means a little more work. If possible, have replacement parts on hand in case you do go a little too far.  

Figure out ahead of time how much material you want to remove. Now sneak up on that amount by removing only half of the unwanted material and then trying the part. Next, remove half of what remains and try again and so on.  

Be careful of surface hardened parts. If you remove the hard surface, the softer material underneath will wear very quickly. Very hard parts may need to be annealed, modified, and then re-hardened.

When you are done, do thorough function checks and test firing.  

You must have a complete understanding of how the mechanism works, how your changes are going to affect the mechanism, what you are trying to accomplish with your changes, and how you are going to accomplish those changes. If you are the least bit uncertain, there’s no shame in sending your firearm out to a specialist.

I got a lot of business undoing incorrect repairs and action jobs. Two young fellows came into the shop with a Smith and Wesson revolver that was giving light firing pin hits. A brief initial visual examination didn’t indicate gross problems with the firing pin or headspace. When I tried the action, I could tell the main spring was weak. I pulled the grips and saw that the strain screw had been backed out. While this lightens the trigger pull, it also weakens the hammer fall. I tightened the screw and explained what had happened. One of their buddies had told them about this quicky action job and they’d tried it. I charged a few bucks and one of them responded, “I could have done that.” So I told them the old joke. The nuclear reactor was about to melt down and the operators were in a panic. The water to the cooling tower wasn’t running. They hit every button on their panels to no avail. They finally called a retired nuclear engineer. He calmly walked to the cooling tower and turned on the water valve. He then presented a bill for $5,000. The reactor operators refused to pay $5,000 for turning one valve. The engineer itemized the bill for them- Turning a valve $1. Knowing which valve to turn $4,999.