Shooting too-soft jacketed bullets not intended for .454 pressures and velocity, when shot at .454 velocity can wash out a forcing cone. OR, bunches and buches of rounds. Some powders can also be more erosive than others.
What does it look like? Erosion, eating away at the rifling, so that the rifling doesn't begin where it used to, but rather, further into the barrel. Often, this erosion can be lopsided if barrel/ cylinder alignment isn't nearly perfect.
Cures? Setting the barrel back and re- cutting the forcing cone, or: re- barreling, or: Taylor Throating the existing barrel.
Shooting .45 Colts in a FA cylinder will not cause erosion in the forcing cone by itself. The damage if one finds it, will be in the cylinder.