You may have a tight neck reamer. Measure your fired brass at the neck. Measure your loaded ammo over the neck. You would like to see north of .003 difference. I prefer .003-.004. If less, you may need to neck turn your brass going forward.
Also, see how easy a new bullet drops into fired brass. If you have to wiggle and force it to slip thru, that's not good.
This is merely folklore Bob.
If necks expand 0.0000000001" it might as well be a mile. The bullet is swingin in the wind, fully released, and there is not 1fps difference from that and any other clearance.
Just think about it: why would there be a difference?
I've done some testing with a fitted chamber, just for the learning here. This, with a remote trigger, and a chronograph.
I went from normal 2thou clearance to essentially none (but no interference). It made no difference. If a neck can expand at all, it's sufficient.
So I ended up sticking with 1/2thou neck clearance. This provided room for a bit of loaded runout, which if high enough to cause a chambered pressure point, which could throw a shot.
Never a problem.
Also, the notions about 'pull force' are meaningless to bullet release.
The fact is: if your load had to push a bullet out of necks, the gun would blow up right there.
You could actually run into this, an interference fitting neck, if you don't mind a building carbon ring at chamber end.
As far as crimping case mouths into bullets? This could be dangerous with highly improved cartridges, regardless of clearances.
