ORIGINAL: driftrider
I load for both .454 Casull and .45 Colt with a set of Hornady New Dimension dies, despite the fact that the die box only says .454 Casull. My seater has more than enough adjustment to seat and crimp .45 Colt nicely. I had the same question until I just went ahead and tried to load .45 Colt with them. They work great.
The only major thing that sucks about using the same dies for both .454 Casull and .45 Colt is that if forced one to adjust the dies every time one switches cartridges, which is both a PITA and it hurt consistancy.
Mike
So go buy a caliper.