mike,

forcing cone erosion "damage" generally occurs from the "abrasive" and "heat" effect of the powder / load used. Lil'Gun has gotten a bad rap, probably, deserved for forcing cone erosion. Think of "erosion", like in the soil, as opposed to damage and you will develop a mental image easier. The presumption is: unburned powder granules and intense heat are directed upon the forcing cone as the bullet transitions from the chamber throat, past the forcing cone, into the barrel. These factors erode "wear" the metal of the forcing cone. The degree of erosion is dependent on the "intensity" of the loads, the number of loads fired, and the rapidity of firing ( strings of fire - think heat ). Also, consider throat "erosion" in other types of firearms. Does this help?
To repair it, generally requires turning the barrel a thread or two or three, realigning the barrel and recutting the forcing cone. Does it really affect accuracy? Usually, only if severe.

Doc