I'm not a 'black rifle' guy but I recently put an AR pistol together and after approximately 20 rounds it had a failure to chamber. Even the forward assist couldn't make it chamber a round. When I took it apart the bolt face was full of brass shavings. I suspect the problem maybe connected to the extractor. What do the experts think? I sure do need some help before I do something wrong and make matters worse.

TIA
Dave in NGA