Here is an old re-post of how to do a simple trigger job to a milspec trigger.
This setup up uses a stock standard lpk, JP spring kit, and a trigger adjustment screw.
Tools required: punch or something to remove the fcg pins, Allen wrench or screw driver to remove the grip screw, sharpening stone (fine), Dremel tool with a cloth polishing bit, polishing compound, locktite, Allen wrench set. You will need a long 2.0mm or 5/64 Allen wrench to adjust the adjuster inside the pistol grip. I use a t-handle Allen wrench for that part of the process.
First step is to break the upper and lower apart, assuming this is a complete rifle.
At this point I always like to dry fire the current setup into my hand a few times to have a feel of how it feels to compare to after.
Next we need to remove the FCG. Remove the pins and pull the hammer and trigger out.
After we have the FCG removed we can see inside the lower. You should be able to see where the pistol grip screw is inserted. This is where the adjuster will protrude out to contact the trigger. Other trigger jobs require drill and tapping of the location. We do not need to do any of that.
Remove the pistol grip screw.
And install the new adjuster screw in its place and tighten down. Looking inside the receiver you can now see how the adjustment screw will contact the trigger.
At this point we are done with the pistol grip screw and adjuster for now, and move on to the polishing of the sear. There are many ways to do this section and you can get much more advanced than what I'm going to cover here. I'm just going to go over the basic polishing that most beginners should attempt.
Start with the trigger, do a good visual inspect and feel the sear face. You should be able to see machining marks, and be able to feel how rough it is with your finger.
Begin with the sharpening stone. It's important to remember we are not removing any metal or trying to change any angles, just smooth it out. I run it up and down the fine side of the stone, with no heavy pressure. Check it every few strokes or so it make sure you are holding it flush, and making a difference.
Looking at it after stoning for a bit, you should see a noticeable difference in the machine marks and how smooth it is. Don't worry about removing all machining marks, just make sure it is smooth. You can see the difference in the picture below, after just stoning for a few minutes.
Now it's time to make it really smooth. Using a Dremel tool with a cloth polishing tip and some polishing compound, polish the face until it is very smooth and shinny, almost a mirror like finish.
We are now done with the basic polishing, and can move on to replacing the springs. Replace the hammer, trigger, and disconnector spring with the ones in the kit. They install just like the factory ones.
After replacing the springs, we can then reinstall the FCG. Depending on how far the adjustment screw was set out from the pistol grip screw, you may need to back it off to get the trigger and pin installed.
Once the FCG is reinstalled, we now can begin adjusting our trigger. Take your long Allen wrench and insert it into the pistol grip screw and seat it on the adjuster.
Adjuster the adjustment screw in until almost all the creep is out of the trigger. I recommend having the safety selector in the fire postition. Once the adjuster is adjusted, cock the hammer back and dry fire into your hand. If the creep is gone or almost gone, check to see if the safety will switch from fire to safe. If it will not, slowly back it off untill it does, then recheck the creep.
On just about every trigger job I have done like this, I have it set to where the safety will not switch and then just backed off enough to clear. If you would like to remove even more play in the trigger you can notch the safety. I have not had the need to do that to achive what I want out of a trigger, but some people do.
After you have it adjusted to where it feels good and the safety will switch correctly, dry fire the hammer into your hand. You should feel a very smooth, consistent, predictable hammer release. Perform a function check to make sure you installed the disconnector correctly, by pulling the trigger and dry firing into your hand but do not release the trigger. Push the hammer back down while you still have the trigger pulled. You should hear a click, and the hammer should stay back, slowly release the trigger and you should hear another click and it should engage the hammer into the fire position.
If the hammer does not lock back, you have an issue and do not attempt to fire this rifle as it may go full auto, multi round burst, or single shot only with needing to pull the charging handle to fire an additional round. If you have this issue, it is not related to the trigger job, but to you incorrectly reinstalling your FCG. Normally a missing or incorrectly installed disconnector spring. Remove the FCG and inspect.
If everything passes the function test, we are now ready to lock everything in place. Remove the pistol grip screw (not the adjuster!). I like to take note or mark the adjuster once I have the pistol grip screw out. Once marked, remove the adjuster and add some locktite the the threads of the adjuster (not the pistol grip screw threads), then reinstall the adjuster to your mark.
Reinstall the pistol grip screw, and then readjust the adjuster making sure again the safety switches correctly with no drag. The re-perform the function test for safety.
At this point the trigger job is complete, lube as normal and work the the trigger by dry firing into your hand. I recommend doing this 100-200 times while you watch tv. Make sure your are letting the hammer land into your hand and not hitting the mag block or bolt release. If your a wuss and the hammer hurts your hand, put something else in its place to catch the hammer like a piece of leather.
The result should be a nice, smooth, crisp, short, consistent trigger pull. After working the trigger for a few hundred pulls, it should get even better. You should know and feel the exact breaking point where it releases. That is the whole objective of a good trigger.
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