by Bob Londrigan, First Published in Front Sight Magazine, July 2017
Part 1 covered trigger installation, setting trigger pre-travel, and setting trigger over-travel. In this article I will cover setting the trigger pull weight, checking/adjusting the grip safety, and checking/adjusting thumb safety operation. As a reminder, anytime you make trigger adjustments you need to do thorough testing in a non-match environment. Test the gun until you can trust that it is functioning properly. DO NOT try to shoot a match with an un-tested and potentially unsafe gun.
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.