My experience has been all of the newer S&W .44 mag. and .45 Colt cylinder throats are substantially undersized as well as Rugers .45 Colts (I have no experience with Ruger .44's).
I agree with others that ideally, the throat diameter should be real close to bullet diameter to reduce leading and maximize accuracy-with cast bullets.
Since all I shoot is cast from my .4X caliber handguns (they are hunting revolvers) I open the throats to .431" in .44 and .4525" in .45 Colt.
I purchased Manson throat reamers for this purpose.
The accuracy increase ranged from noticeable to substantial, leading is not an issue. This with cast bullets obviously.