Re: RCBS Small base dies
I've loaded thousands of rounds for AR-15s, M1 Garands, M1As and FALs; I used regular RCBS FL dies on all of them, and I never crimped one single round. I've never had a problem asociated with using this approach, either.
IMHO, unless you're loading brass that was fired in a machine gun, you do not need Small Base dies for a gas gun. The only ammo I have ever crimped is ammo for lever actions and revolvers.