Hey guys, trying to find a forum for a CMMG question and AR15.com seemed like it had the best industry area.  

I have a CMMG 5.7 bolt and barrel kit, 5” barrel. Installed in standard upper and using a standard lower with their conversion mags.

The issue is this: Gun will cycle fine for the first couple (first few maybe), no issues, but when you insert that 2nd or 3rd mag (or maybe 4th) and drop the bolt and then fire… the first chambered round out of the mag will fire but the bolt won’t unlock. There will be basically no recoil as the bolt does not unlock and there is no reciprocating movement. The next shot - after you manually cycle the bolt - will often result in more movement of the bolt, it appears to unlock and begin to reciprocate, but still sometimes it doesn't fully eject or pick up a new round, and then by the 3rd round it is fully operational again and running smoothly. There is no issue with feeding or the bolt seating.

I have swapped the barrel to a different upper, I have gotten a new bolt and bolt carrier from CMMG, I have sent it into CMMG (they shot a magazine or two and it didn’t malfunction and sent it back), and I have tried different ammo and buffer weights. I have tried the original mags as well as the new replacement mags, mags full or half empty, I have gently polished the back of the bolt lugs and ensured no burrs on the barrel extension, I have changed the extractor spring.

It does the same thing regardless of all of those variables. It seems that it is literally the bolt not effectively doing its 1/16” or so rotation and then unlocking.

My only though is that maybe my barrel extension locking lugs are incorrect, particularly the bottom two that use a slightly different profile than the others. Anyone able to send a photo of their barrel ramps and extension?

Thanks for any insights or help.