You should be fine. At the pressures you're loading lead bullets to, it won't cause you pressure problems. Unless your chamber is exceptionally tight (unlikely with a Ruger), you won't have chambering issues either. You will likely find the bullets seat a bit harder because your expander die will be expanding for a .452 bullet, but again, with lead bullets it won't matter much. Your finished rounds will just have a bit of a 'waist' underneath where the bullet stops in the case. Depending on the size of your chamber mouths (Rugers tend to be a bit tight for 45 Colt, unless they've opened them up in the past couple of years), you may actually find that you get better accuracy and less leading with the .454 bullets. If that is the case, and you want to stick with that size, RCBS sells a .454 expander that is included in their CAS dies. It fits fine into the regular RCBS expander die. Will make seating plain-base bullets a bit easier, but won't make much difference if you load bevel-base.