Odd AR-15 problem..

[Al Thompson]

A young friend of mine just purchased a lower and added an upper. The rifle is 5.56 with various upper parts assembled by the previous owner. Looks like a GI barrel and a well done but unknown BCG.

The lower is a well known brand with factory trigger parts. I will not name the brand as I have two of the same and zero issues. That's one of the reasons for my post as I'm stumped, due to my extensive positive use of my lowers and my recommendation that he purchase the same brand.

Here's what he's reporting : when he fires a round from the bench, the rifle fires two or more rounds. When he's prone, no such issues. Ammo was Brown Bear. He said that it felt like when he fired a round, as he released the trigger, it would fire again or even fire a short burst of three rounds.

Thoughts?

 

[Tirod]

Sounds like bump firing.

It's done by allowing the weapon to recoil enough that when it returns to the forward, original position it presses the trigger into the finger and fires again.

 

[W.E.G.]

Hold the gun harder.

 

[DougW]

I agree with Tirod. Maybe the shooter needs to pull the rifle in a bit tighter.

Disconnector spring?

 

[taliv]

i guess position might have something to do with it...

but you DEFINITELY need to do a function check on that rifle before he shoots it again.

odds are, replacing the disconnector will fix it.

(edit: and every body puts out a lemon once in a while. heck, i've even been less than happy with a BCM part once or twice, and i had a noveske that wouldn't hold the bolt open on empty mag. sample size is everything, you know)

 

[rklessdriver]

taliv is dead on. Check the disconnector to make sure it's holding on to the hammer. Easy to do once you have the upper and lower seperated.

That's quite dangerous to have the disconnector malfunctioning.

A man recently went to JAIL when the ATF charged him with possoession of an unregistered machine gun for a similar problem.
Will

 

[ugaarguy]

Perhaps bump firing, and a slightly out of spec disconnector?

Here's the USGI way to function check it:
1) Make sure it's unloaded (obviously)
2) Charge the weapon
3) Pull trigger AND hold it to the rear
4) With trigger still held to the rear charge weapon
5) Release trigger
- If trigger does not reset you have bad juju (probably the disconnector) with the fire control group. Pop the takedown pin and pivot the receivers apart - If the hammer is forward there's definitely a problem (again likely the disconnector).
- Repeat test several times to ensure it's not an intermittent problem caused by a damaged or out of spec, rather than completely broken, part.

 

[Float Pilot]

We had that happen on some Air Force M16s that were converted to sorta M16A2s using parts kits from the lowest bidder. (Billy-Bobs storm door and rifle part company)

Occasionally while some poor troop was trying to qualify they would get another round going off while releasing the trigger. Sometimes a short burst.

It turned out to be that the spring legs had not been installed on top of the trigger and sear assembly thru-pins. And since the pins were junk and undersized, they walked over to one side and let the inner assembly tilt over just enough to cause the problem.
A proper re-assembly fixed the problem, even with the crappy parts.

 

[kwelz]

Sounds like a Disconnector problem. What brand are we talking about here, I know you don't want to mention but some brands are known for certain issues whether your particular samples have or not. Or it could be a one off problem. But the more info we have the easier it is to diagnose the problem.