^^Don't use a once fired case. Believe it or not, they can shrink upon firing. Take that once-fired brass and throw it across the room. It's confounding you and not important.

Just make the bolt close on a go gauge and not close on the no-go. At that point, all is good. You should now be able to insert a live round and it closes on it and extracts it. Next, fire that round. It should go "boom" and make a big hole in your wall, I mean target.