Randy,
As you know, Freedom Arms recommends a .45C cylinder for use with .45 Colt ammo in the .454. Some think this is just to make money. I seriously doubt there is enough money in extra cylinders to make much difference. I asked a few respected members of various forums, and they pretty much said it was a good idea to get the .45 Colt cyl if shooting more than just an occasional .45.
I shoot a lot of .45 Colt and load them on a Dillon 550. In order to load 454s, I have to change out the primer feed assembly (large for .45, small for .454). Being basically lazy, I decided that it would be easier from a loading perspective to get an aux .45C cyl for the .454.
Anyway, rather than worry about the potential problems (real or imagined) associated with the use of .45Cs in the .454, I had FA fit an extra .45C cylinder while they had the gun for the firing pin upgrade. I wish I would have had the cyl fluted at the same time – just a personal preference and an quick way to see which cyl is in the gun.
And yes, I do use both cylinders.
Paul