I have a new Midwest Industries Billet upper with a new FA BCG and a new YHM 300 Blk barrel.  All parts were cleaned and well lubed with CLP.  Manual cycling without magazine attached, everything works fine.  Placing 1 round of 147g ammo in magazine and charging, BCG fails to move completely into battery Pulling the charging handle back, doesn't extract the round the first time but it does the second time it is pulled back.  Ammo case has a little nick in the rim and a scuff on the bullet.  Swapped a SA BCG out of another AR with the FA BCG in the 300 Blk and everything works as designed with this one.  Put the FA BCG in a 5.56 barreled DPMS upper and it does exactly the same thing.     Any ideas on what might be wrong with the FA BCG?  I've taken it apart, cleaned an lubed the heck out of it and manually moved the bolt in and out until it operated smoothly.

Maybe it's the bolt itself.  Lugs out of spec, burred, etc..  The only real difference between FA and SA BCG is the carrier, so I would inspect the bolt itself closely.

 

it sounds like the case rim may not be getting past the extractor on the feedstroke. the extractor has to open up a bit so that it can slip over the cartridge rim and get properly positioned to allow the bolt carrier to seat properly and allow for extraction.

I'm swapping out the bolt to see if that is the issue...I have a spare, then I'll check the extractor and let you know. Thanks.

So I swapped the bolt. Fixed the issue.  Upon close inspection of the suspect part the extractor appears to be the issue. Ejector spring was binding really bad