Brain Storm on rare AR prob

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[ARCHIVED THREAD] - Brain Storm on rare AR prob

Posted: 9/15/2010 8:48:34 AM EDT

Just got a customers AR built and system checks were all good, fired 3 rounds through it before I handed it off. He gets home and gets 4 rounds out the pipe and tells me it did not fire, but there was a live round in the chamber. Said he could push the trigger forward and then it would fire in that situation. I thought right away either I screwed up the spring installing or it was faulty. Told me at first there was no pin strike on the primer what so ever. Then the next day, he said he saw a slight strike on a round that failed to fire. I took the lower apart and ensured everything was good, function test was good, parts seemed to be good to go. He goes back home and has the same issue. So about every 3 - 4 rounds he is getting a fail to fire. I'm down to wondering if the bolt is not seating correctly, which I will be looking at today at the range, or something is wrong with the firing pin......

Anyone have any issues like this before? I have not seen anything like it in the 5 years I have been building these for people.

Thanks

Posted: 9/15/2010 8:50:04 AM EDT

[#1]

This was the case with 2 different types of ammo being LC and Wolf

Posted: 9/15/2010 9:30:36 AM EDT

[#2]

Going to put one of my lowers on to see if it is a disconnector problem with his, and attempt to isolate the problem..... just odd that it function tests fine with the upper off...

Posted: 9/15/2010 9:37:23 AM EDT

[#3]

Stag LPK?

Posted: 9/15/2010 9:38:34 AM EDT

[#4]

Have him slap the FA every time he chambers a round. Maybe the buffer spring is getting hung up?

Posted: 9/15/2010 9:41:07 AM EDT

[#5]

I have dealt with something similar on a friend's rifle. I tossed in a new BCG and he has been gtg ever since.

Posted: 9/15/2010 9:41:25 AM EDT

[#6]

Is a rock river kit in a charles daly lower. Never had an issue like this. If it is a seating issue, I will see that right away.

Posted: 9/15/2010 9:46:30 AM EDT

[#7]

Are you able to replicate the problem?

When the FTF happens, is the hammer dropping?
Is the trigger pin walking?

Posted: 9/15/2010 9:56:55 AM EDT

[#8]

Trigger spring is too weak or the sear has a burr on it, preventing the trigger from resetting and a weak/wrong/upside down disconnector spring. Sounds like it's slipping off the disconnector and firing when he pushes the trigger forwards...

Posted: 9/15/2010 9:58:55 AM EDT

[#9]

I am taking him to the range in just a couple minutes, the spring is in correctly for the disconnect, and I did not observe any burring either. The stock assy I ordered with the upper from Stag as well. I will update when I get back. Hope to have it fixed for him by then though!

Posted: 9/15/2010 11:07:46 AM EDT

[#10]

One of my lowers has a VERY short pull single stage trigger (maybe 5 mm). When I first put it together, about ever one in 25 shots the trigger would fail to reset and I'd have to push it forward, then I could pull it. Is that what he's talking about re having to push the trigger to get it to fire?

In my case it was the disconnector not letting go due to a tiny tiny burr that just took a quick polishing to fix, then some breaking in in front of the TV. It hasn't happened again in the last 2000 rounds.

Posted: 9/15/2010 11:57:08 AM EDT

[#11]

Put a new triger, hammer, and safety in and it worked great. Going to look the parts over when I get time. Put a different disconnect spring in and it still screwed up, so it wasn't that. Hard to say, but could have just been something out of spec with the disconnector, hammer perhaps. Sending it back to Rock River tomorrow for them to check out. First RRA kit that I have had an issue with in 3 years of using them.

Posted: 9/15/2010 12:24:29 PM EDT

[#12]

Interesting.... I had the EXACT same issue with an RRA LPK kit I installed on a recent build. Once I swapped the disconnector out with a extra DPMS one I had (left over from a trigger upgrade on another build), no more problems. I still can not see with the naked eye where the issue is on the RRA one.

Posted: 9/15/2010 12:47:15 PM EDT

[#13]

Grab some 1000 grit sand paper or a polishing stone and slightly polish the disconnector hook, this will remove any burrs it has and should solve the problem.

Posted: 9/15/2010 2:51:00 PM EDT

[#14]

I had the same problem recently. Except a primer had gotten into the lower and would randomly engage the safety.... I was this (holds fingers together) close to trading it in until a buddy blew it out with some air. The blown primer popped out of the lower onto the floor, and we just stood there dumbfounded.

Posted: 9/15/2010 2:55:35 PM EDT

[#15]

Quoted:
Grab some 1000 grit sand paper or a polishing stone and slightly polish the disconnector hook, this will remove any burrs it has and should solve the problem.

+1 usualy, but I don't see anything with the naked eye on this one. I am sure at this point though that it was a jacked up disconnector.

Posted: 9/15/2010 2:58:14 PM EDT

[#16]

Quoted:
I had the same problem recently. Except a primer had gotten into the lower and would randomly engage the safety.... I was this (holds fingers together) close to trading it in until a buddy blew it out with some air. The blown primer popped out of the upper onto the floor, and we just stood there dumbfounded.

Had that with a brand new 6920.

Posted: 9/15/2010 3:16:04 PM EDT

[#17]

Wolf ammo.

I wouldn't consider anything wrong unless the rifle did this with brass cased SAAMI or NATO spec ammo. Wolf ammo is the bottom of the barrel.

Posted: 9/15/2010 3:54:50 PM EDT

[#18]

Quoted:

Quoted:
Grab some 1000 grit sand paper or a polishing stone and slightly polish the disconnector hook, this will remove any burrs it has and should solve the problem.

+1 usualy, but I don't see anything with the naked eye on this one. I am sure at this point though that it was a jacked up disconnector.

Disconnector test: pull trigger and hold back while depressing the hammer (should make contact with disconnector and latch.) Release trigger (disconnector should still hold back hammer.)

Sometimes when pushing down on the hammer and resistance is extremely tight there is room for improvement of disconnect contact surfaces.

Sorry if you have already used this test and I am playing Captain Obvious here.

Posted: 9/15/2010 5:03:49 PM EDT

[#19]

i would have thought weak spring would be the first thing to look at..

Posted: 9/15/2010 5:13:36 PM EDT

[#20]

Quoted:

Wolf ammo.

I wouldn't consider anything wrong unless the rifle did this with brass cased SAAMI or NATO spec ammo. Wolf ammo is the bottom of the barrel.

Believe it or not, it's not the worst stuff you could buy...

ETA: i've had less problems with Wolf Military Classic than some brass-cased brands.

Posted: 9/15/2010 5:27:33 PM EDT

[#21]

Quoted:
Wolf ammo.

I wouldn't consider anything wrong unless the rifle did this with brass cased SAAMI or NATO spec ammo. Wolf ammo is the bottom of the barrel.

...and if you look at his 2nd post it says they tried both Wolf and LC.

Posted: 9/15/2010 6:42:37 PM EDT

[#22]

Just above the notch in the hammer material is removed from the hammer to clearence the front of the trigger. I have seen that not done properly and cause problems with the trigger resetting.

Posted: 9/16/2010 5:09:18 AM EDT

[#23]

Check the pistol grip screw and see if it is projecting into the lower receiver and tying up the disconnector.
Shorten the screw about three threads and you should be good to go if that is the problem. HTH

[ARCHIVED THREAD] - Brain Storm on rare AR prob

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