I've had a store bought 556 for years but recently finished my first build - 7.62x39 - don't flame or attack with the "just buy an AK" I've heard and read it plenty.  I was wondering if someone local had a complete rifle (non-pistol) that has been through the trials of function issues.  I think I'm at the adjust the gas and/or buffer stage, but it'd be nice to talk it through with someone knowledgeable.

Hit me up if you're near New Bern.

Most 7.62 russian ARs suffer from reliability issues.  If i was in the market for on I'd look very close at the cmmg mutant rifle.

My dad panic bought a 7.62x39 Colt AR for me when I was 2. It runs 100%. The Achilles heel of the 7.62x39 AR is magazines. The only magazines I've ever used that worked 100% were preban era franken mags, where someone welded the bottom of an AK or mini-30 mag to the top of an AR mag. The bolt face is also kind of wide; some say bolts break more easily.



ETA: If I were wanting a 30 caliber AR15 for terminal performance/hunting rather than for cheap plinking, I'd consider 300 blackout instead. Similar ballistics, and a whole lot of the annoying issues of 7.62x39 AR15's are solved.

I'm not near New Bern but I can try to answer any questions.

I built one and am very happy with it.  I used an AR Stoner barrel/bolt combo and a cheap adjustable gas block.  I'm also using AR Stoner mags and as long as I only load them to 25 rounds they work great with no malfunctions so far.  I have almost 300 rounds thru it.  

I'm also working up a subsonic load for it.  It groups a 200 gr bullet pretty good, but I'm having trouble getting it to cycle.  I'm to the point of having to change out and possibly shorten the buffer spring.

To be clear, I put adjustable gas blocks on every AR I build.  They reduce recoil, keep everything cleaner, and in my opinion reduce wear and tear because the bolt carrier is not slamming back so hard.

All- thanks for the replies.

Drizzle - Thanks, but unfortunately I had already decided on this route and had all the parts in hand by the time I heard of the mutant - a day late and now many dollars short.

Couch Commando - I wish I could have found a Colt 7.62 while I was building this rifle.  I'm using ASC mags right now and I don't think they're the problem, but more testing will tell.  I do need to smooth the lips on the mags cause they are scraping the shat out of my rounds.  Lastly, the 300 blk is way more expensive ammo than 7.62 russian.  Edit - reread your post, yes hunting/target 300 blk would be better, but i built it to shoot a lot.

25-06Shooter - thanks for the input, I was thinking I would start with the adj gas block rather than keep adding heavier sping and buffer weights.  I have read about many 7.62 builds that, once they were dialed in, were just as reliable as any 556 build.

My primary problem is that after 3-5 rounds of correct function it will lock up with the bolt about halfway closed with a live round in the chamber.  I was reading that to be really excessive bolt bounce, what do you think?

After some tweaking of the magazines a bit I didn't have the bolt get stuck anymore.  I was able to manually cycle dozens of rounds with the charging handle.

OK so I stripped it down and did a super thorough cleaning on it, Lubed it up, Took it and my Del-Ton 5.56 out Saturday and did some test shots.  My daughter shot 5 shot strings from the 5.56 as a control so I could watch the bolt and ejection.  As always, it functioned flawlessly.  Then she fired three rapid 5 shot strings from the 7.62 and they all went great, with a few weak 2 o'clock ejections.  With only 11 rounds left in that caliber, I put 5 in one mag and 6 in the other.  The first five went great and then of course I got off 4 before a FTE (eject) jam.  The 5th round not fully chambered due to the 4th not leaving the ejection port.  I had planned on using the H buffer from the 5.56 to see if it improved things, but it was running good until the last 2 rounds.  They fired OK but 2 in a row doesn't tell me much.

So... I'm ordering an adjustable gas block hoping it will slowdown the bolt.  It seems it is starting the extraction/ejection too soon, before the case is ready.  My gas port is carbine length and .075" which is in tolerance with the manufacturer's dimension.  

Any thoughts?

I'm in Midland - I built a 7.62x39 upper about a month ago with the components listed below. The only thing I did was disassemble & polish the entire bolt carrier (already NIB) + polished the M4 feed ramps to a nice shine (after assembly). Runs everything 100% - except Silver Bear hollow points hang up (they have a monster HP compared to others). I'm using C-Products mags - only have a 5 & 10 round right now - 20's are currently on backorder.

Build: Spike's upper with M4 feed ramps, Tactical Ambush bolt carrier group with enhanced firing pin & Fail Zero NIB coating, Tactical Ambush 16" carbine length with M4 feed ramps, standard YHM low pro GB, Anderson lower, standard mil-spec buffer tube, cheap standard Tapco buffer & spring, Bushmaster LPK with standard springs (had JP yellows - caused light primer strikes).

Could be the Fail Zero NIB coated BCG that helps this thing run so well? Might be worth buying one for around $ 110. As you can see - I didn't use anything special for this build, some of the parts were even used.

Thanks for the reply.  I have the NIB Failzero BCG from TA.  (I actually have 2 and they both have the same issue)  

For the build I used a complete TA upper and started with an 80% lower.  I used CNC to finish it and after I used calipers and micrometers to verify it is machined correctly, I also pinned my Del-Ton upper on it to double check it, and it works great.  I also used a PSA LPK except I subbed in the ALG ACT FCG.  Buffer tube is PSA standard as is the spring and a basic carbine buffer.  

Maybe I need to polish my BCG, although the NIB is the smoothest I have ever used.  Did you polish inside where the bolt rides?  If so, what did you use?  The fact that you have the TA 16" carbine length barrel and yours runs fine is throwing me off.  I was really thinking I was over gassed, but that would be decided by the barrel, and we have the same barrel.

ETA: Did you happen to measure your gas port diameter before you assembled the upper?