Kinda depends on the actual groove dia. of your barrel. I dont know how the .45C H&R barrels are running on this, there used to be quite a variation in Colt's barrels, some at .454ish.
Now, sizing down a .459 to .454 will be stiff if you use anything harder than wheelweights to cast, and dont water quench them!
Short answer is 'maybe'. Either way, if you want to spend the money on that sizer die and, if needed' nose punch (dont know how you are sizing) it should be the right one for CAST bullets (not the jacketed bullet 'std' dia.) in your bore, that would be groove dia. at min.
FWIW, buy a LEE double cavity .45C mould to start with. Cast of WWt metal, pan lube, load and try as cast, no sizing.