300 black sub help

Hello, so I’m trying to fix up my uncles .300blk but am stumped. He just got his supressor out of Jail, a gunwerks 6 supressor. This thing runs supers great, but I cannot for the life of me run subsonic Ammo. Tried multiple Ammo brands and grains. It’s a 16” faxon 300blk. Currently on lightest buffer at A5H0. Gas block is non adjustable. It will cycle out the old round, but will not cycle a new one. At this point would it be a gas port being too small? Or something else. Any feedback would be great.

What exactly is it doing?

Is it short stroking or maybe it is over gassed and the bolt is returning forward before the magazine spring can push the next round up. Have you tried a heavier buffer just to see how it behaves?

Possibly it is under gassed in which case it would need a larger gas port. Any possibility the gas block is installed off center?

Gas block is lined up properly just check that, and I believe it to be short stroking. The very first round the bolt locked back on the edge of the mag, not the bolt catch, and every round after that the bolt just went home instead of locking open. It ejects the current round but dosnt throw them very far at all almost like they are barely making it out. Then won’t cycle next round. I started with an A5H2 buffer unsurpassed and it wouldn’t cycle (didn’t have supressor on hand) then moved to A5H1 with supressor and wouldn’t cycle, then moved too current A5H0 and now it will eject round but won’t pick second up. Just seeing if there’s any quick fixes that can be done or if it’s a new barrel or drilling gas hole.

Sounds like the gas port was drilled to run super Sonics only…might check with Faxon on that.

Carbine gas system?

What size is the gas port?