[mrerick]

A frosted steel surface is one that has been etched by a corrosive compound. It is no longer smooth polished steel (iron and carbon) grains.

Polished steel grain on gliding (bullet bearing) bullet surfaces change to rough steel and oxide pits on gliding surfaces - this changes the friction coefficient of the relationship and changes the ballistics of the barrel.

Frosting would logically slow the bullet down slightly, generate more heat and leave more residue on a frosted surface. Is it significant? Probably not at close range. Probably not when just firing a few rounds...