AR 15 Fails Function Check

[Kilber]

I am trying to troubleshoot one of my AR builds that is failing a function check. Here are the symptoms:

Charge weapon, weapon on safe, squeeze trigger, hammer does not fall.

Charge weapon, weapon on fire, squeeze trigger, hammer falls.

While holding the trigger, charge weapon, release trigger, hear a "clunk".

Now for the failure:

While holding the trigger, charge weapon, release trigger SLOWLY, hammer falls. The disconnector will catch if the trigger is simply released, but if I slowly release the trigger, the disconnector fails and the hammer falls.

I have tried reseating the disconnector and spring, but this has failed to resolve the issue. Any ideas?

[m16]

Are you sure you installed the disconnector spring correctly?

One end of the spring is bigger, if you install it upside down you will have issues.

[vintagearms]

Make sure disconnector spring is installed correctly. (fat end down) or its a bad disconnector/hammer.

[CK_32]

Is this a home build?

Double check you installed everything correctly. Like above FS really easy to swap springs and run into issues.


This is why you guys should label or divide baggy your LPK gun companies. A bag of parts is a pain in the a** for new and experienced builders. Would make life so much easier if self fire group had a bag. And the hammer spring was in another. Just a small thought for any LPK makers that might read this.

A little bit goes a long way. Would really appreciate it and not have to fish and separate my LPKs before ever build and triple check before I start. Would also help packaging on the assembler line and cut back on the double or missing parts being each bag should have x amount and this LPK group.

[Kilber]

Are you sure you installed the disconnector spring correctly?

One end of the spring is bigger, if you install it upside down you will have issues.

The spring is installed correctly.

[m16]

Is this an 80% lower?

Maybe try another trigger out of a lower that passes the function check.

[dut]

Sounds like the problem I was having recently. My rifle would fire twice; pull trigger AND release of trigger.

This didn't start happening right away, previous two shooting sessions were fine.

New disconnect spring didn't help.

I didn't want to deal with anymore troubleshooting, so I just bought an AR Gold trigger.

My guess is maybe my Stag LPK trigger was 'polished' (or whatever they do) too much?

[TheDigitalPicasso]

I've geared of people having this issue before and when you shoot with live ammo you weapon will double fire.

Lol the guy above us the person I was talking about^^^^

[BrianRodela]

Your disconnector interference with the hammer catch isn't enough to catch properly. The disconnect or needs to pivot forward more but rests on a stop forward of the trigger pin. By removing very little material through stoning that surface, it will allow the disconnector to pivot forward more, engaging the hammer more and allow the sear to become more engaged when the disconnector finally releases upon trigger release.

[Kilber]

Your disconnector interference with the hammer catch isn't enough to catch properly. The disconnect or needs to pivot forward more but rests on a stop forward of the trigger pin. By removing very little material through stoning that surface, it will allow the disconnector to pivot forward more, engaging the hammer more and allow the sear to become more engaged when the disconnector finally releases upon trigger release.

Thanks for pointing that out, I'll check it out when I get back to my to my redneck gunsmithing later tonight

[TheDigitalPicasso]

Contact Stag and have them replace it.

[jgraham15]

Your disconnector interference with the hammer catch isn't enough to catch properly. The disconnect or needs to pivot forward more but rests on a stop forward of the trigger pin. By removing very little material through stoning that surface, it will allow the disconnector to pivot forward more, engaging the hammer more and allow the sear to become more engaged when the disconnector finally releases upon trigger release.

I would not recommend this advice to anyone that isn't intimately familiar with the ar15 trigger and how it operates.

This may be far fetched but let's say you modify your trigger, take it to the range and after a few rounds it starts to double or worse it does a full auto mag dump. If someone were to inspect your rifle and notice you have modified the trigger in any way you may be asking for a world of trouble as you are now in possesion of an illegal class 3 rifle. The fact that you clearly modified that trigger could be held against you in the courts and you could be looking at a felony and a whole lot of time hanging out with bubba in a very small cell.

Now maybe I need to loosen the tin foil hat a little but at least think about it for a moment before you start screwing with that trigger.

[Kilber]

Does anyone have theory on why the release speed of the trigger would cause the failure? Why would the hammer only fall when the trigger is slowly released, and catch when the trigger is "just let go"? Maybe it has to do with the inertia, since the force of the springs when tension is abruptly removed able to cause JUST enough force to push the disconnector into the catch position, but not enough "umph" when slowly released?

[BrianRodela]

You have to look at the amount of distance the trigger sear must travel up to come in contact with the hammer when the disconnector actually releases. It appears that as the disconnector releases, there is still a gap that allows the hammer to miss the sear and continue forward. When you release the trigger quickly, the momentum of the trigger allows it to close this gap in time enabling the sear to engage the hammer.
I would suggest checking out some animation videos to fully understand the trigger, never hurts! Also something to keep in mind. Although lower receivers are supposed to be machined to spec, deviations in both manufacturers and production lines do happen. If the trigger and hammer pin holes are off by even a few thousandths, this will affect performance of the trigger and its interfaces. I soon discovered this when I changed out my lowers from a S&W to a JD machine. I had to readjust the match trigger considerably to get it to function properly. If the tolerances are off in your lower, simply replacing the disconnector with the same factory one may not solve the issue and the trigger should be adjusted for your lower. As jgraham15 pointed out(and its good advice) this should be done by someone who has a good knowledge base and understanding of the AR trigger, but also is not difficult to learn.
If you have FaceTime, I'd be happy to show you.

Brian

[tal3nt]

Might as well check for broken pins too