I think the .455 Colt is on the short side as regards case length, yes? Or is it the other way...

I do know that when I got some Fiocchi .455, the cases were so short versus my stash of CIL/ Dominion cases, that I had to shorten my seating/crimping die. Don't remember any more how much, but it was significant- maybe 0.080-0.100"?! (As they were originally .45 Colt dies, they're now REALLY short- lock ring about has no theads to engage.)