45 Colt in the 454 Casull
First, the 45 Colt is not precisely a shorter version of the 454. The 45 Colt has inherited from BP days (via SAAMI) an over sized chamber and some what loose specs on cartridge diameter. This problem was corrected with the 454 which has tighter chambers and tighter cartridge diameter specs. You will occasionally find a 45 Colt cartridge that will not chamber in a 454. This is the reason 45 Colt dies are not recommended for loading the 454. On the other hand, if you are going to load 45 Colts for your 454, use 454 dies. The fouling ring left by a shorter cartridge can raise pressures when shooting the longer cartridge. The 454 is already pretty close to the wall pressure wise so it's important to clean properly anbs well after using 45s in it. My persoanl preference for 38/357, 44 Spl/Mag, 45/454 types is to always use the longer case, even for midrange loads.