Got some once fired brass I'm working with. Most of this stuff is letting the pill drop right down through the neck. A couple I can't even crimp enough to grasp the cannelure, I've squashed a couple cases already trying. It's mixed brands.
-Brass worn too thin?
-Not sizing right?
-Need a crimp die?
-Roll newspaper around each bullet to make up the difference and jam it in the case anyway? (a vote for this one might tarnish your credibility)