Check your gas block/tube by using airfrom an air hose or a can, put a fired. Brass shell in the chamber and blow it thur the gas tube end inside the upper reciever. Make sure you plug the end of the barrel.. if the brass case come out ... That's NOT your problem !
Then check the ejector and extractor.
Good Luck. You may need it !
I fixed a Black Thorne rifle once they Loctited so much stuff
and didn't tighten anything right. Loose handguard ,replaced ejector spring.
Installed springs backwards, gas block wasn't aligned. Took me 3.5 hours to make it right..