Without all the mumbo jumbo.
S/S McGee said: Sometimes first fired brass can cause a problem on another's reloading bench.
The OP never stated or made clear where the brass was originally gotten or who fired it. (Be it someone else or him. Who knows? ) So I based my theroy on: The brass in question was fired originally by another person and not from the OPs weapon.
With that said I can't remember ever having the ability of chambering someone else's first fired brass directly into the chamber of my rifle and not have its bolt lock up without difficulty. EVER!!
"That's my story and I'm sticking to it!!"