DIY Lightening and smoothing up you factory AR trigger

[TheDan]

The AR triggers and hammers are only surface hardened - most after market parts are different - after you break the surface, the metal is not hardened.

What type of surface hardening do they use?

 

[Dawico]

The AR triggers and hammers are only surface hardened - most after market parts are different - after you break the surface, the metal is not hardened.

That is my experience with hardened metal I have worked with. Get through the surface and it is night and day difference. But the surface is a real bear.

Not saying they are not hardened, it just doesn't seem like it.

 

[TacticalPandaBear]

That is my experience with hardened metal I have worked with. Get through the surface and it is night and day difference. But the surface is a real bear.

Not saying they are not hardened, it just doesn't seem like it.

Very rarely are the triggers and hammer not case hardened, but I'm glad you at least recognize that and warned of the risks of doing this modification. I've seen enough malfunctions from modifications like this that I just tell people to use extreme caution. I used to work at a range where there was a runaway gun because they did a trigger modification similar to this.

Just be careful!

 

[TheDan]

I suppose someone could use something like this:
http://www.brownells.com/gunsmith-t...dening-compound-sku083000033-27119-52952.aspx

It's going to matter if your fire control parts are MIM or low carbon forgings/millings, too.

 

[bptactical]

Not trying to piss on anybodies thread but....................................................This thread is terrifying.
I cannot think of a faster way to create an unsafe/dangerous weapon.
Before doing trigger work you need to understand a few things about the trigger mechanism:

There are three types of sear engagement, negative, neutral and positive.
Negative sear engagement is where the hammer moves forward during movement of the sear, a very dangerous condition that creates erratic sear let off resulting in inconsistent trigger break. It also means that the hammer is not reliably secured by the sear and can disengage without warning.
Dangerous as hell and can lead to doubling, mag dumps and in the worst case out of battery ignition which can be catastrophic and cause injury or death. During the recoil impulse the sear may not catch or "bounce" off of the hammer causing the hammer to follow.
Don't do it.

Neutral sear engagement is where the hammer does not move at all as the sear is moved, meaning the two faces are perpendicular to each other. Not ideal but considerably safer than negative engagement. You can get a somewhat decent trigger with neutral sear engagement but again it is not overly consistent and precise.

Positive sear engagement is where the hammer effectively moves rearward (cocking motion) during sear movement. The reason I say "effectively" is this movement must be virtually non perceptible. You should not see rearward movement of the hammer and if you rest your finger on the hammer you should feel only the absolutely slightest rearward movement. In extreme cases you can actually see the hammer move rearward.
This results in a very hard trigger pull because besides the trigger having to overcome the pressure of the trigger spring, it now has to overcome the camming action of the excessive positive angle PLUS the tension of the hammer spring.
You want slight positive angle, it is the safest and provides the most positive and consistent sear engagement.

THE ANGLES OF THE SEAR FACE AND SEAR SURFACE OF THE HAMMER MUST NOT BE ALTERED!!!
This cannot be stressed enough, you are dealing with a firearm and the consequences of poor workmanship can injure and kill.

Without a jig or fixture maintaining the correct angles is difficult to say the least.
The CORRECT way to address a crummy AR trigger is by polishing of the engagement surfaces (without changing any angles) and by adjusting the sear engagement "depth".
Polishing is straightforward, but 200 grit is waaaay too coarse, you are not trying to remove any material, just smooth what is there. A fine India stone or in a pinch a piece of flat glass and 1000/1500 grit wet or dry paper wet with kerosene or diesel will work fine. You just want to remove the tooling marks. When the sear face is polished just very lightly break the corner of the search face/top of trigger.
Now for the sear depth.
Look at the hammer, see the sear surface on the bottom of the hammer? If you cannot see where the sear surface of the trigger engages the sear surface of the hammer take a Sharpie and color the sear surface on the hammer. Reassemble the hammer and trigger in the lower and cycle it a few times.
Take it apart and you should see a contact pattern for the sear/hammer surfaces. Ideally you want to see about .020-.025 of engagement but you will usually see .030-.050. This is too much for a decent trigger and results in that long and creepy take up.
Slowly and carefully take a small amount of material off of the outside part of the hammer at the sear surface. Keep everything square. Reassemble frequently and check.
Do not go less than .020 of sear engagement for safety reasons.
You will be pleasantly surprised with a nice, smooth trigger and just a touch of take up prior to breaking.
There is a huge difference in 5# of gritty, long trigger and 5# of crisp, clean break.
Oh and Panda is dead bang on, triggers and hammers are just case hardened, cut through that tough skin and the nice trigger goes away quickly and can result in doubling etc.
Please be careful people and if you do not understand the dynamics of a trigger system, the kitchen table and sandpaper is not the place to learn.

 

[Dawico]

Not trying to piss on anybodies thread but....................................................This thread is terrifying.
I cannot think of a faster way to create an unsafe/dangerous weapon.
Before doing trigger work you need to understand a few things about the trigger mechanism:

There are three types of sear engagement, negative, neutral and positive.
Negative sear engagement is where the hammer moves forward during movement of the sear, a very dangerous condition that creates erratic sear let off resulting in inconsistent trigger break. It also means that the hammer is not reliably secured by the sear and can disengage without warning.
Dangerous as hell and can lead to doubling, mag dumps and in the worst case out of battery ignition which can be catastrophic and cause injury or death. During the recoil impulse the sear may not catch or "bounce" off of the hammer causing the hammer to follow.
Don't do it.

Neutral sear engagement is where the hammer does not move at all as the sear is moved, meaning the two faces are perpendicular to each other. Not ideal but considerably safer than negative engagement. You can get a somewhat decent trigger with neutral sear engagement but again it is not overly consistent and precise.

Positive sear engagement is where the hammer effectively moves rearward (cocking motion) during sear movement. The reason I say "effectively" is this movement must be virtually non perceptible. You should not see rearward movement of the hammer and if you rest your finger on the hammer you should feel only the absolutely slightest rearward movement. In extreme cases you can actually see the hammer move rearward.
This results in a very hard trigger pull because besides the trigger having to overcome the pressure of the trigger spring, it now has to overcome the camming action of the excessive positive angle PLUS the tension of the hammer spring.
You want slight positive angle, it is the safest and provides the most positive and consistent sear engagement.

THE ANGLES OF THE SEAR FACE AND SEAR SURFACE OF THE HAMMER MUST NOT BE ALTERED!!!
This cannot be stressed enough, you are dealing with a firearm and the consequences of poor workmanship can injure and kill.

Without a jig or fixture maintaining the correct angles is difficult to say the least.
The CORRECT way to address a crummy AR trigger is by polishing of the engagement surfaces (without changing any angles) and by adjusting the sear engagement "depth".
Polishing is straightforward, but 200 grit is waaaay too coarse, you are not trying to remove any material, just smooth what is there. A fine India stone or in a pinch a piece of flat glass and 1000/1500 grit wet or dry paper wet with kerosene or diesel will work fine. You just want to remove the tooling marks. When the sear face is polished just very lightly break the corner of the search face/top of trigger.
Now for the sear depth.
Look at the hammer, see the sear surface on the bottom of the hammer? If you cannot see where the sear surface of the trigger engages the sear surface of the hammer take a Sharpie and color the sear surface on the hammer. Reassemble the hammer and trigger in the lower and cycle it a few times.
Take it apart and you should see a contact pattern for the sear/hammer surfaces. Ideally you want to see about .020-.025 of engagement but you will usually see .030-.050. This is too much for a decent trigger and results in that long and creepy take up.
Slowly and carefully take a small amount of material off of the outside part of the hammer at the sear surface. Keep everything square. Reassemble frequently and check.
Do not go less than .020 of sear engagement for safety reasons.
You will be pleasantly surprised with a nice, smooth trigger and just a touch of take up prior to breaking.
There is a huge difference in 5# of gritty, long trigger and 5# of crisp, clean break.
Oh and Panda is dead bang on, triggers and hammers are just case hardened, cut through that tough skin and the nice trigger goes away quickly and can result in doubling etc.
Please be careful people and if you do not understand the dynamics of a trigger system, the kitchen table and sandpaper is not the place to learn.

I fully expected these comments about this thread and I don't think working on a trigger is for everybody.

Plus now that good replacement DIY triggers are readily available and getting cheaper I hope nobody tackles a project like this that can't handle it.

I appreciate the extra information and recommendations for smoothing up a standard trigger. I also have no problems with extra warnings for those that are going to attempt it. Working on any part of a firearm can lead to unsafe conditions and each individual must calculate the risks of doing so.