The RCBS .454 dies resize tighter and are made to closer tollerances than what they use in the .45 Colt dies. Also, the crimp part of the seater die is different. If you go to Freedom Arms web site, check on their section for reloading they explain why you should use specific dies for the the .454. But....to your question. I do not see any reason why you could not use .454 to work with .45 Colt....but (you knew that was coming, didn't you) the .454 case is somewhat longer than the .45 Colt so you might not be able to crimp properly with the .454 seat/crimp die. The only way to know would be to try it and see what happens. My best guess is that it will work just fine in crimping as does the .357 Mag and .44 Mag dies do with their "littel sisters." The only disadvantage that I can think of the .454 sizer may be oversizing the .45 Colt case slightly as .45 Colt chambers are usually a bit larger than the FA .454 chamber, but for normal accuracy I doubt that you could tell any difference.
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