The $0.50 AR Trigger Job

The Designer Of The AR Series Rifles, Eugene Stoner, Was A Genius.
There are about six (6) upgrades that will make the AR a world beater instead of a utility rifle. This upgrade goes a long way toward addressing one of them.

Mr. Stoner had to design a trigger system that was safe above all else.
Most of the solders of the day were acquired by means of the draft, and couldn't keep a job flipping burgers at Burger Doodle...
And with todays 'Lawyer Proof' manufacture, things haven't progressed much.
The trigger is safe, and because of that trigger, anything down range is safe also!
This is a way to update that trigger so you don't need a four foot long hydraulic ram to get the rifle to fire!


THIS UPGRADE SHOULD NOT BE ATTEMPTED BY ANYONE THAT DOESN'T HAVE A CLEAR AND COMPLETE UNDERSTANDING OF SAFETY, CYCLING & FUNCTION OF THE AR SERIES RIFLES.

This Page IS NOT Intended For Amateurs!
Failure To Properly Execute This Upgrade Can (And Probably Will...) Result In Serious Injury Or Death.
This Upgrade Is Best Done By A Qualified Gunsmith!! Print This Article And Take It To The Gunsmith.

Proper Safety Precautions & Function Testing Are An Absolute Must For This Project.
If You Do Not Possess A Through Knowledge Of The Trigger Group Design, Function & Cycling Proceeders, And Safety Cycle Proceeders,
DO NOT ATTEMPT THIS PROJECT!

Defer This Upgrade To A Properly Qualified Gunsmith!

YOU MUST TEST ALL SAFETIES, INCLUDING TRIGGER SEAR ENGAGEMENT, DISCONNECT ENGAGEMENT, TRIGGER BLOCK SAFETY AND IMPACT TESTING.




There are Three (3) Issues with the Factory Military style triggers in AR (and it's clones) rifles,
1. Extremely Long & Grinding Trigger Pull,
2. Trigger Pressure Actually Has To Increase As The Trigger Moves Toward Release,
3. There Is NO Provision For Adjustment From The Factory.

The Factory Trigger Group Parts were (and are) investment casted, the sear surfaces were ground, and the parts were case hardened. There are no exceptions to this rule that I know of.
I know people that paid over (US) $100. for a 'Trigger Job', when all that was done was grinding on the sear surfaces.
This is a bad thing... Grinding ('Honing' or 'Stoning' if you prefer) of case hardened parts simply removes the hardened metal, and in a very short period of time the so called 'trigger job' has revealed it's self to have ruined the trigger and hammer totally.

You CAN NOT Cut, Grind, Machine, Stone, Hone or otherwise remove the very thin case hardened metal and expect the trigger and hammer to survive. Period.
THERE ARE A VARIETY OF AFTERMARKET TRIGGERS ON THE MARKET, All of which are an improvement on the factory military style trigger group in the AR series rifles.
Cost ranges between (US) $100 to $500, and most are well made, safe, relatively easy to install and function well.

HOWEVER, Nothing is made for plinking and hunting rifles that an average guy can purchase for a few bucks.
That's where this upgrade comes in...
I started doing this in the '70's (yes, I'm an old fart...) after a surplus AR-15 I had purchased didn't quite live up to expectation, and the local so called "Gun Smith" ruined two sets of trigger & hammer sets trying to do a 'Trigger Job'.
Later, I did this in the military to my issued M-16, and I always scored 'Expert' when it was time for record fire.
Non-invasive, reversible, requiring NO modification to the receiver, and only affecting the trigger it's self, this modification is truly an 'UPGRADE'.



MAKE SURE THE RIFLE IS UNLOADED!

You will need...
1. A 1/4"x20 set screw, 1/4" long. About $0.50 at the local hardware store.
2. A hex wrench ('Allen' wrench) that fits the set screw.
3. Flat blade screw driver (remove the grip screw).
4. Metal scribe or fine point marker.
5. Round file or small rotary grinder (Dremel Tool).
6. Thread locker (Locktite Blue works very well).
7. 1/8" Long nose punch.
8. Hack Saw Blade. If you need to shorten the grip screw, a hack saw is a good way to do it.

MAKE SURE THE RIFLE IS UNLOADED!

Remove the top end of the rifle via the attachment push pins.
The top end of the rifle is not needed, and will be in the way during upgrade and testing.

Seperated Rifle ... Grip Removed Detent & Spring
Click on images for more detail.

Pull straight down on the hand grip after the screw is removed, as pulling it to the rear of the rifle will bend the spring securing the safety selector.
Be careful not to loose the safety selector spring or detent pin.
You may have to shake loose the safety selector detent. They like to bind in the holes.


Safety Slector Removed
Click on image for more detail.


With the hammer in the reward or 'cocked' position, you should now be able to work the safety selector out of the left side (right to left travel) of the receiver.


Bottom Of Lower Reciever
Click on image for more detail.

This images shows where everything came from, and hopefully, goes back to...!


Set Screw Insertion
Click on image for more detail.

Now take note the back of the trigger DOES NOT intrude into the cross hole where the safety selector was just removed from.
This will have to be reproduced once the slack is taken out of the trigger.


Once the grip and safety selector are removed, insert a 1/4"x20, 1/4" long set screw into the grip screw hole from the bottom. The illustration above shows what and where.
---That is a 1/4" in diameter, 20 threads per inch, 1/4" long---
Some clones will have a different thread size or pitch, but all AR's and most clones will have 1/4"x20 threads.

If you have a 'Dry Fire' device to catch the hammer, this is a good time to install it.
If you don't, you can always catch the hammer with your fingers, since we are just tripping the trigger/hammer sear and the hammer doesn't have to actually go forward to strike anything.
You will immediately be resetting the hammer in the 'Cocked' position, keeping a finger or thumb on it to catch it will be natural anyway.

Insert the screw with the hex wrench until the back of the trigger starts to move.
Continue to insert the set screw SLOWLY until the trigger releases the hammer...
That's the Set Screw tripping the trigger, not your fingers...

Set Screw Nose
Click on image for more detail

This is the inside of the lower receiver, with trigger removed, showing where the set screw will protrude to take the slack out of the trigger position.

CATCH THE HAMMER! DO NOT let the hammer strike your receiver!
Allowing the hammer to strike the receiver can (possibly) crack the receiver, deform the back of the magazine well, and will certainly elongate (oval) receiver holes for the hammer pivot pin.

Back the set screw out about 1/2 turn, and cock the hammer again.
Check the trigger for release travel.

If you want more travel, back the set screw out some more, if you want to reduce more of the travel, insert the set screw.
Test several times so you get a feel for the adjustment of the trigger.
You may want to temporarily replace the hand grip (without springs or screws) for better feel.

WARNING! I shouldn't have to give this warning to someone competent, but here goes anyway...
You MUST leave enough sear engagement so there is a positive, safe & solid catch of the hammer.
There must be enough sear engagement to resist accidental discharge, either through something brushing the trigger, or by dropping or impacting (bumping into) the rifle.
This is best determined by a professional, and is an ABSOLUTELY NECESSARY PRECAUTION.


This upgrade DOES NOT change the amount of force required to pull the trigger, just the length the trigger has to travel.



NOW, Test the disconnect.
The disconnect is the small piece with a hook on top, sticking out of the slot in the top of the trigger piece. It's held in place by the trigger pivot cross pin.

Hold the trigger to the rear, and cock the hammer.
The disconnect should catch the hammer, and you should have to let up on the trigger to allow the trigger engage the hammer sear notch.
If the hammer gets away when you release the trigger, you have an off spec trigger group.
(This is pretty common in rifles that are not AR or Colt factory.)
Your disconnect will have to be 'adjusted'...

The disconnect piece is stamped, and the manufacturers dies are often off spec, or just plain worn out.
This piece often has material clinging to the shear line where it was stamped, and that is often the problem.

To remove the disconnect, use the 1/8" punch and tap out the trigger pivot/retaining cross pin.
Remember, the disconnect is held in place with this same pin.
With the pin removed, you should be able to remove the disconnect for hand fitting.

Light filing in the indicated area will often clean up the shear line and cure the problem.
GO SLOW! And check for function often. Don't remove any more material than you absolutely have to for correct function.


Now, at this point, you should be able to cock the hammer, and use the trigger to release it with a noticeable difference in travel.
The trigger should be able to catch the hammer no matter how fast you move it to the rear, or if you hold it backwards and let it slip from under your finger (referred to as 'Side-Stepping'). If the trigger won't catch the hammer each and every time in simple testing, it's never going to function correctly during full speed firing action.

Test the disconnect by holding the trigger fully to the rear and cocking the hammer.
When the trigger is released, the disconnect should release the hammer, and the hammer should be caught by the trigger sear.
If this happens correctly each and every time during testing, you may move on to the next step.


Safety/Trigger Interface
Click on images for more detail.

This image shows the adjusted trigger protruding into the safety selector hole.
This intrusion must be corrected.

Mark the back of the trigger that is showing through the cross hole for the safety selector.
You can use a metal scribe, or a very fine point felt tip pin.
The material showing in the hole must be removed from the trigger.
Removing this material will allow you to use the factory safety selector.
DO NOT TAKE ANY MORE MATERIAL OFF THAN YOU HAVE TO.
This is not a race, take your time, go slow and do smooth, neat work.

Once the trigger is marked using the safety selector hole as a stencil, use your 1/8" punch to remove the hammer pivot/retaining pin. It simply pushes out.
You may need to tap the pin out, BUT DON'T BEAT ON IT! There is a spring retainer holding the pin in, but it shouldn't be too stubborn.
Set the hammer and hammer spring aside.

Once the hammer is out of the way, you can remove the trigger spring with the same 1/8" punch.
BE CAREFUL! The trigger and disconnect are both being held in by the same pin.

Trigger Modification
Click image for more detail.

Once removed, you may grind or file away the material you marked that was sticking in the safety selector hole.
You have done the job correctly when the trigger and trigger pivot pin is in place, and you can install the safety selector.


Now, remove the trigger once more, and use your hex (allen) wrench to thread the set screw in EXACTLY one OR two threads and apply one drop of thread locker.
Give the thread locker a few seconds to migrate into the threads, and back the set screw out EXACTLY as much as you screwed it in.
Once the thread locker has become tacky and the excess removed, you are ready for reassembly.

Another note for making the trigger action smoother is to use some 'Action Grease' on the sear surface of the hammer and trigger before final install.
Replace the trigger, disconnect, hammer and safety selector, and make sure everything works correctly and as described above.
Remember, the 1/8" punch makes a good alignment tool for the hammer, which can be tricky to hold in place and get the pivot pin in when you only have two hands...

It's a good idea to function and safety test the trigger group before you reinstall the hand grip, so if the set screw needs to be fine tuned, it's easy to get to.

When installing the grip, you may have to shorten the grip screw.
This isn't a big deal, and a hack saw blade does the job in short order. Be sure to dress the threads with a file, sand paper or emery board before reinstalling.


If you decide to reverse this procedure, the only thing seriously modified was the trigger, and it's easily replaced or a spot of weld or braze will restore the surface you filed on.