I've loaded 45 ACP and .357 Mag, I crimped both. It seems to me that it would be a '' MUST DO '' , for two reasons.
1. to push the bell back in(as you found out).
2. I think the crimp is needed to get the mouth of the case turned in just a hair so the edge of the case mouth is not catching things as you load.
I'm not an expert, but I thought I'd pitch in. You ought to see what some of the more experienced loaders have to say.
Good luck loading!!!