by Bob Londrigan, First Published in Front Sight Magazine, May and July 2017
The parts of your trigger group that may need maintenance from time to time are your trigger, hammer, sear, sear spring, disconnector, hammer strut, and hammer spring. Once installed and set up properly the trigger, disconnector, hammer strut, and hammer spring usually will not need much maintenance or adjustment besides cleaning, lubrication, and checking for breakage/wear. If you changing or modifying other components in the gun, however, you may have to check these trigger components at that time also. At that time, it would not hurt to double check them for fit and proper function. The main components to worry about as far as wear and needing adjustment are the hammer, sear, and sear spring so I will cover those in depth. I will also go over initial setup of the actual trigger itself as well as safety functions to check both before and especially after you do any work to the gun.
Before starting any work you need to assemble the tools you will need. If you are going to do any type of work on your trigger you should have on hand a trigger pull gauge. I like the Lyman digital model but any type of trigger pull gauge is better than none. A gauge comes in handy not only for measuring the trigger pull weight but also to measure the pre-travel weight which is a key to getting the trigger pull just right. You will need the tools to disassemble your grip – punches, hex keys, wrenches, hammer, etc. The one tool you will need that might not be in your toolbox is a 0.050 hex key to adjust trigger over-travel.
Once you have your tools you are ready to get to work. Let’s talk about how to install the trigger. You might be replacing a trigger with a broken bow or changing to a different profile or length. In any case, you will need to get it installed properly. You will need to completely disassemble the bottom end to get the trigger in. You will need to have the grip off the gun and the magazine release removed. Once installed the trigger needs to move freely in the channel in the grip with very little play. It should be loose enough to move back and forth without resistance. To get this fit, you may have to adjust the trigger shoe and/or the trigger bow a little. The shoe may need to be fitted on the top and bottom surfaces and maybe even on the sides. Go slow with this adjustment until the shoe will go into the grip without dragging. If the shoe starts to go in and then you feel drag check the trigger bow width. You may need to squeeze it a little to narrow the width. Check with a caliper before and after. You should only need to narrow it a few thousandths. If it is too narrow, it may drag on the magazines so check that too. Once you have the trigger moving smoothly, screw the overtravel screw out a few turns just so you are sure it won’t be contacting the mag release when you are ready to start making adjustments. The overtravel screw is the small screw in the trigger. When it is screwed in it contacts the mag release. The further it is screwed in the less the trigger can travel to the rear. As you look at the front face of the trigger screwing clockwise reduces overtravel and counterclockwise increases overtravel.
You can put the grip back on the gun at this time. Once the grip is back on and the grip screws are tight, check the trigger one more time to make sure it slides smoothly in the trigger channel. Sometimes tightening the grip screws can cause it to bind. If it does bind, check to see what dimension is tight and reduce accordingly until the trigger glides freely with the grip screws tight.
Now that you have the trigger installed you can check the other components. When doing work on the internals it is easier to see what is going on if you do not install the thumb safety and grip safety. First check your disconnector. All bearing surfaces should be lightly polished, and the head should slide freely in the hole in the frame. The sides of your hammer and sear should also be lightly polished. This is to make sure there is no resistance to movement. You don’t want to remove material -- just make sure the surfaces are smooth. Do not adjust the mating surfaces between the hammer and sear. This should be left to an experienced gunsmith. If those surfaces are not cut properly the gun will need to be repaired before making any adjustments. The adjustments we are doing are just to get the gun setup to run the best for you. Install all the parts and then you are ready to make final adjustments. There are three things to check/adjust: trigger pre-travel, trigger over travel, and the actual trigger pull weight. Thereafter you must check to make sure all safeties function properly.
Pre-travel Pre-travel is defined as the distance the trigger must move before the trigger bow pushes the disconnector enough to contact the leg of the sear. You will feel this as you pull the trigger. It should move smoothly until you feel it stop. (Test with the hammer cocked). Continuing to increase pressure will eventually drop the hammer. The amount of pre-travel that is best for you is a matter of personal preference. Some people like a large movement and some prefer to keep it to a bare minimum. You will need at least enough so that your hammer still catches in the halfcock notch. On most guns, this minimum is going to be around 0.035 inch. Set the pre-travel to your preference by bending the tab on the forward portion of the trigger bow. Bending the tab forward reduces pre-travel. It is easier to adjust this with the trigger out of the grip so you may need to assemble and disassemble several times to get it right. Use a caliper to measure the distance between the trigger guard and the face of the trigger.
Monitor that distance as you bend the tab. This will tell you how much you are moving the trigger. Once you have the distance right make sure you test to see if the hammer will catch on the halfcock notch. Test this by cocking the hammer and then holding the hammer while pulling the trigger to release the hammer.
Lower the hammer slowly while releasing the trigger. The hammer should catch at halfcock, and if you pull the trigger should remain captured. If it does not pass this test put a little more pre-travel in until it does. If you start with at least 0.035 inch pre-travel you should not have a problem.
Overtravel Overtravel is defined as the distance the trigger moves after the sear releases the hammer. It is adjusted by turning the small set screw in the trigger. Test by cocking the hammer, then holding the hammer and pulling the trigger. Continue holding the trigger back while rocking the hammer back and forth. You should not feel the hammer bumping anything. Continue to adjust the screw in (clockwise from the front) until you start to feel the hammer bumping the halfcock notch or until you pull the trigger and the hammer does not fall. At this point, back out the screw until you feel no contact and then add another ½ turn for good measure. The overtravel should now be adjusted.
I have a few additional precautions before we go over adjusting the trigger pull. You should not attempt to adjust your trigger pull unless you fully understand how the parts involved work and interact with one another. You could end up with a gun that is unsafe. When a gunsmith does a proper trigger job, he cuts the angles on the hammer hooks and the sear so that they interact in a precise manner. Most gunsmiths will have angles and hammer hook heights that they have developed over the years and determined through testing to be the most reliable. These angles and heights are often different for different trigger pull weights. Light trigger pull weights usually require something different from heavy trigger pull weights. For this reason, it is not a good idea to try to reduce your trigger pull just by bending your sear spring unless you are very familiar with how the sear and hammer in your gun are cut. If on the other hand, you are replacing parts you will not have much choice but to adjust the sear spring because every hammer and sear are little different. Also, hammer and sear hole placement in frames will vary somewhat and change the engagement geometry between the hammer and sear.
The sear spring has three legs. Looking at it from the back – the left leg controls the amount of pressure holding the sear in the hammer hooks. It is responsible for most of the trigger pull weight. The middle leg puts pressure on the disconnector. It controls how much weight the pre-travel has and returns the trigger and disconnector to position after trigger reset. The right leg does not contribute to the trigger pull weight as it only controls the amount of pressure needed to deactivate the grip safety.
You will need a trigger pull gauge to adjust the middle spring. The pull weights are so light it is hard to tell what you are doing without a gauge. Before adjusting the middle leg of the sear make sure you have set the pre-travel and over-travel of your trigger. Bend the middle leg of the sear spring to adjust the trigger pull weight during the pre-travel phase of the trigger pull. You want at least 8 oz. of pressure on the middle leg. You measure this with a trigger pull gauge: cock the hammer first, then pull just hard enough to get the trigger to start to move making sure that it does not bottom out. If you have more than 8 oz. you may be able to reduce your trigger pull a little by bending the middle leg of the sear spring. Adjust it down to 8 oz. and then check the disconnector reset. You do this with the slide removed. Cock the hammer and then push the disconnector down and release. The disconnector should have firm tension on it and pop back up to its original position with no sticking at all. If you do get some sticking check to see what is causing it. You will have to correct this or add more pressure to the spring to overcome the sticking. The disconnector must reset crisply every time for reliable operation of the gun.
If you are installing a new sear spring and need to adjust it, start with the right leg and adjust the pressure on the grip safety. Then adjust the middle spring as we covered above. Finally, adjust the left leg until your trigger gauge reads the setting you want for your total trigger pull. When replacing the sear spring on a gun where the trigger group was functioning properly, I would measure the trigger pull with the old spring first and then set the new spring to match the same trigger pull weight within a ¼ pound or so. Don’t try to go lighter if you don’t know how the hammer and sear angles are cut. If you are installing a complete trigger group that is already cut, check with the manufacturer for their recommendations on setting the trigger pull weight.
Once you have the trigger group installed and adjusted, you must check the grip safety and thumb safety for proper engagement/operation. Check the grip safety first. If the thumb safety is installed take it out first. Check the grip safety with the thumb safety out of the gun so you can look inside the gun and see what is going on. A good trick is to put the thumb safety in part of the way from the opposite side to hold the grip safety. If you have an ambi safety, you would just need to put in the right side only. The tang on the grip safety should drop down behind the trigger bow and block the trigger bow from moving enough to drop the hammer. If the tang will not drop down to block the trigger bow, you will have to remove enough from the end of the tang so it will.
Go slow and take off a little at a time until it does. A small amount of movement of the trigger bow is ok. You just don’t want the trigger bow to move enough to start moving the sear. If you have adjusted the pre-travel on your gun and shortened it, there is a good chance you will have to adjust your grip safety tang.
Next take your grip safety out and check your thumb safety. There is a tang on the thumb safety that blocks the sear from moving when the safety is rotated up into the engaged position. If you have installed a new hammer or sear, there is a good chance that you will have to adjust this tang. If it is too long, you will need to take off a little at a time until the safety will rotate up into position. The tang should block the sear and not allow any motion at all. If you see any motion of the sear at all, you will need to make the tang a little longer by peening some metal over to fill the gap.
This will only work if it is close. If you need to do much more than a few thousandths of an inch, you will have to start with a new safety.
A final reminder, whenever doing any work on your trigger group make sure to check that all safeties are working properly post-adjustment. Then test fire the gun to make sure that everything is functioning safely. To test fire, start out with one round in the gun just in case there is a problem. Work up to two rounds, then three rounds, etc. until you are confident in the safe functioning of the gun.