I don't own a P22, so there-
But as a general rule, dry-firing rimfire guns can lead to peening of the chamber's edge, since the firing pin (which just hits 'air' in a centerfire that's dry-fired) actually is designed to crush the rim against the chamber's edge. Without the rim, the firing pin hits the edge of the chamber and eventually breaks, peens the edge of the chamber or, if you're the lucky type, both.
Larry