Are they? I have shot quite a bit of 45 Colt through my mdl #83 and it seems to like them. Why doesn't FA want 45 Colt brass in the 454 cylinder? Because of the resulting higher pressures from stuffing 454 rounds in on top of the crud ring after having shot 45 Colts in it?
I always shoot the 454 first and then shoot the 45 Colt ammo. I seriously doubt it would let me chamber any 454 rounds after 45 Colt anyway because the chambers are so tight. Heck, my 83 rejects close to 50% of that Winchester 250 gr JHP (Hunting) factory 454 ammo even when the guns sparkling clean. I got like 6 or 7 boxes of it with the gun. I needs the brass and hate to have to pull it down.