.45 ACP Smiths have different rifling than usual for Smiths (six lands and grooves compared to standard five lands and grooves). Further, the .45 ACP grooves are much shallower. This is for a reason and goes back to the first ones issued in WW I. Apparently, the rather hard jacketed bullets of military ammo had a tendency to occasionally stick in the barrel during early experiments in converting the revolvers to .45 ACP. They came up with the shallower rifling (and six lands and grooves) to combat this problem.
I shoot nothing but cast bullets in my two 625's (625-6 with 5" barrel and a 625-8 JM Special with 4" barrel). I think that Smith is cutting rifling with electro-discharge machines. Whatever process they are using, they sure shoot well (and with cast, also).
FWIW
Dale53