View Full Version : Trigger Job on .308 AR

10-15-2011, 11:54 AM
Hey guys,

Just tried doing a partial trigger job on my .308 AR. Well, as for right now, I only did the spring work to lighten up the pull. It worked really well. I have a Timney 4lb single stage in my AR-15 and compared to that, I'm guessing it's probably around 5lb's now from the 9-10lb's it used to be.

My only complaint is that there seems no way to adjust the trigger's pull length. Even though it is a smooth pull all the way to the disengagement point, it's still a long pull and introduced a lot of "creep". Being that it is a single stage trigger, ideally, there should be NO creep and just disengage when you start to pull. Now, I read about something to eliminate the creep, and that is to buy a longer Pistol Grip screw that will pop through to the inside of the receiver FCG area and stick out a little bit. When sticking out at a proper distance, it will keep the rear of the trigger from falling all the way back down, making it so that the pull length is extremely short.

I tried doing that and it worked, however it introduced another issue. Let me explain: Without the upper installed, when you push back the hammer all the way while holding down the trigger completely, then release the pressure on the hammer, it will stay back due to the engagement of the disconnector. When you release the trigger afterwards, the disconnector disengages and the hammer moves forward slightly, but is then held back via the front of the triggers engagement point on the bottom of the hammer. This whole process is what allows for "semi-auto" functionality. But when I did this little trick with the pistol grip "set-screw", it made it so that the hammer would be caught by the disconnector correctly, but when you release the trigger thereafter, the hammer would only be caught by the front of the trigger's engagement point about 50% of the time.....the other 50% of the time the hammer would continue to fall all the way (therefore potentially causing doubles, triples or even full auto slamfires). I believe this was caused by 1 of 2 issues:

1) Either my spring lightening job on the trigger spring caused the trigger to not reset fast enough to hit the engagement point of the hammer or
2) I screwed in the pistol grip screw too far, thus making the trigger not return far enough to hit the hammer's engagement point consistently enough.

I suppose a 3rd option could be a combination of the two, but I dont know.

So my question: Does anyone know a way to decrease the pull length on a standard AR-15 trigger without causing issues to the disconnector/trigger engagement point?

I wish I could draw a picture if none of this makes any sense. It's much easier to understand what i'm talking about if I could show you in person, but this is the best/only way i could describe the problem.

Thanks for any help/guidance.

Scott Connors
10-15-2011, 11:59 AM
The simplest and safest way is just to install a Geissele trigger of your choice. Issue AR triggers are only surface hardened, so if you should remove too much metal you may end up with an unregistered machine gun, which would be a bad thing, especially with a .308. Don't risk it.

10-15-2011, 12:04 PM
The simplest and safest way is just to install a Geissele trigger of your choice. Issue AR triggers are only surface hardened, so if you should remove too much metal you may end up with an unregistered machine gun, which would be a bad thing, especially with a .308. Don't risk it.

Like I said, I havent done any metal/surface polishing yet. I understand the potential issues at hand :)

Doing a trigger job is one thing.....intentionally attempting to make a machine gun by altering the trigger group is another. The often misunderstood Olofson case was the latter.

10-15-2011, 12:09 PM
Everyone was recommending Bill Springfeilds trigger jobs to me when I was lookin to fancy up my AR.


I personally haven't tried him yet, but seems like an option. May have to give him a call one of these days since I got a spare FCG laying around.

What about a Timney trigger as a drop in?

10-15-2011, 12:22 PM
Jard and be done with it!

10-15-2011, 6:17 PM
Naa, I like learning and this is a fun project that is cheap and it's already showed good results. I understand that I can get a good trigger from Timney, Jard, Geiselle, and others. I have one in my AR-15. I will probably end up going with one of those sometime in the future for the .308 AR, but my wife has another baby on the way and I really cant be spending any money right now, especially with Christmas right around the corner. I figured this is a good way to try to get a better trigger out of what I already have, and I get to learn a little more about getting more out of a standard AR-10/15 without spending any extra money.

It's an extra FCG anyhow, so what does it matter :)

10-15-2011, 7:53 PM
A better way to control the overtravel of the trigger is a 1/4-28 set screw threaded into the pistol grip screw hole. This allows independant fine tuning of trigger adjustment without resulting in a loose pistol grip. I typically set the screw so that the disconnector just barely releases the hammer to the sear when the trigger is released, then back the screw out another 1/4 to 1/2 turn to ensure the adjustment works every time. I also add a small amount of locktite to the set screw prior to final adjustment just to make sure everything stays set.

For the rest of the trigger job, I follow more or less the standard 15 minute trigger job:
-Cut one leg of the hammer spring off completely.
-Bend both legs of the trigger return spring up about 10-20 degrees to reduce spring tension and lighten trigger pull.

I also go a bit further and bob the hammer, completely removing the spur portion and rounding off the top of the hammer. Although supposedly only surface hardened, this operation requires the use of a cut off wheel on a dremel as the hammer material, even under the surface, will dull a hacksaw blade almost instantly. Bobbing the hammer will restore some of the velocity lost by cutting the hammer spring. I havent noticed an issue with light primer strikes on any 5.56 or 7.62 NATO ammo as of yet, although some 7.62x39 ammo has had issues lighting off with this trigger job.

Finally, I polish the hammer/sear engagement surfaces using a cotton polishing wheel with some fine polishing compound. I've found that automotive paint buffing compound works pretty well for this. It's fine enough that it's nearly impossible to polish through the surface hardened layer of the hammer and sear. During assembly, I use a small amount of white lithium grease on the surfaces to further reduce friction. The end result is typically a rather short single stage pull with little creep that breaks at around 4 to 5 pounds