by Bob Londrigan, First Published in Front Sight Magazine, May 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 am going to break the article here and then go over how to set the actual trigger pull weight and check/adjust the grip safety and thumb safety operation in the next issue. As always, when 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.