300 Blackout getting stuck in the chamber

I've got a radical firearms in 300 blackout. Unfired rounds are getting stuck in the chamber and are really hard to extract. But ONLY when loaded from a magazine. If I load a round into the chamber manually and send the bolt home... no problem.

Slide a round into the chamber then turn the barrel up, round falls free instantly.

If I load a magazine and send the bolt home loading a round in the chamber, that's when it gets stuck. With or without the magazine, it's still dang near impossible to extract.

I tried a different, known good BCG, and it was still almost impossible to extract.

I honed and polished the chamber. Still nada.

I tried with and without the o ring in the extractor. Same result.

Type of magazine doesn't change the result either.

I'm scratching my bald head over this one...

Any help is greatly appreciated.