[FlyFish]

This issue has been discussed several times on various forums. I have the same problem, as do many others. The problem appears to be when the retaining spring rises to push against the case rim as the shellplate moves to the resizing station, tipping the case mouth out (i.e., away from the hub) enough to allow the mouth to catch on the entrance to the sizing die.

The root cause(s) seem to be a combination of slightly more clearance under the shellplate than is necessary for the case rim to slide in/out, which is what leads to the tipping, combined with certain brands of dies that have less relief (radius) at their entrance. In my experience, RCBS dies in particular have this problem (great dies otherwise - just not optimal for the LnL AP).

One fix that I've read about, which I'd call more of a kludge, is to stretch the retaining spring so it doesn't press so much against the case rim. I've also heard of reloaders with lathes, and the knowledge to use them, who've taken a bit off the base of the shellholder so as to decrease the clearance where the shells fit in, but I don't know how well that works. Alternatively, I've found that I've gotten pretty good at keeping my left index finger ready to push misbehaving shells back into alignment as they enter the resizing die for those calibers that are particularly problematical for me.