So for my new AR build i decided to have some fun and make it a 7.62x39 and, ironically, it feeds flawlessly and rarely has a light primer strike (which i know are common problems), but about 1 out of every 10 rounds will eject and load a new cartridge fine, but the trigger won't reset (hammer forward).  

Gun info:
Lower is standard spikes with psa lpk
Standard carbine buffer in spikes tube w/ spikes spring
ALG ACT fcg
Faxon 7.62x39 16" barrel with midlength gas system, low pro gas block (came with barrel), and spikes gas tube.
Rubber city armory standard bcg wit 7.62 bolt, Red X enhanced firing pin

Originally i had a heavy (spikes T2) buffer in it, i figured between the mid length gas system and heavier buffer maybe we were under cycling just enough to not always reset the trigger, so i swapped the buffer out for a standard carbine buffer.  Its maybe a little better, but not much.  

I've looked over everything close and nothing in the fire control group, bcg, or gas system appears to be wrong as far as i can tell (im no expert by any means).
I've been using cheapo Tula ammo mainly, but i also tried some brass (sorry, don't remember specs, it was some of my buddies loose surplus) and i didn't seem to make a difference.
I've been keeping her well cleaned and lubed.  Probably about 200 rounds through her.
Anybody got any ideas?

Lpk  isn't functioning properly

Is the large end of the disconnector spring down inside the trigger?

this

As it's only happening 1 in 10, I doubt it's the fire control parts but it might be the fire control finger.

Are you sure your not riding the trigger? Full press and full release? Maybe a little bump fire?

Just double checked, large end of disconnector spring is down.  No problem there.  It has yet to fail a function test with the upper off, seems to catch and reset smoothly like it should.  I've had no such problems when i'm shooting other ARs, so i don't think its my technique.

Change the trigger / hammer.  I'd wager the interface if FUBAR.

The hammer is riding the bolt forward?

I had a new Spikes build I did a while back the with NiB FCG and would get a dead trigger where it was locking back. I'd have to push the trigger forward to physically reset it.  

After about 100-200 rounds it worked itself out.

Perfect since.

Sounds like a fairly similar situation, i've got the same Nib coated trigger set-up.  I'm going shooting this weekend, so i'll take it with me and run a bunch of rounds through it, see if it smooths out.  Thanks for your input

Hope it does. It was an odd thing. Didn't happen often but enough that I could expect it to occur at least once a mag for the first few hundred.


Pull the trigger, round would fire. Dead trigger. Would have to put my finger behind the trigger, push it forward to reset and it would be fine. Could never "see" anything wrong with it. Can't remember if I was able to reproduce it with the upper off.


Either way, by about 150-200rds it went away. Figure it just needed some smoothing out at some of the contact points.

Had one do the same exact thing. Had to push the trigger forward a few times and no problems since. Couldn't se any burrs or anything wrong but there was. It was like there was a primer or something trapped in the disconnect but found nothing. Still going strong and hope it stays that way. I'm sure it was in the hammer/trigger and even ordered a LPK to replace it.