Rich 2.0 wrote:
either the chambers dirty and needs cleaned or polished or you got some real crappy ammo
sounds like its not going into battery all the way and when the hammer hits the bolt its forcing it to go the last few millimeters and locking it up ... try different ammo first
Talked with Steve at Bushmaster today and he said it could be one of many things, like---dirty ammo, dirty bolt, dirty chamber OR the chamber might need reamed out a tad and polished. My local guy at The Gun Store looked it over and measured everything with a micrometer and said everything looked good to him. He didn't have a "go-no go gauge"....So...guess it's going to get a reaming
in the near future!
I was going to ask what gun/barrel but that's been answered. What buffer weight? I'll bet 'carbine' buffer? What are you lubricating the BCG with?
DPMS and Bushmasters are notorious for having tight chambers, so you'll probably need to have it reamed.
I don't believe laquer is an issue anymore, it was in the past though based on what Russian crap had on casings. The issue is likely a combination of overgassing and a tight chamber. Overgassing will cause the bolt to unlock early while the casing is still partially obturated in the chamber. With steel cased ammo this is worse, as it does not expand/contract as quickly as brass. This results in the partially obturated (expanded) casing being torn instead of cleanly extracted from the chamber. Typically, the gun will run but you'll see accelerated extractor wear and damaged cases. But overgassing, combined with a tight chamber, would definitely result in a lockup like you describe.
If you send it off to be reamed, have them check gas port dimension. On a 16" carbine, anything over .076" is overgassed. Nothing much you can do at that point, except run a heavier buffer.