Does dry firing harm my P7M8?
^^^^ What he said. Snap caps are cheap. Firing pins, not so much. The P7 series firing pins are very easy to replace, which is nice. On many other semiauto pistols, they can be very difficult to 'skilled gunsmith only' territory. The Beretta M9/Model 92FS comes to mind.+1 for snap caps only. I have Azoom snap caps for every firearm I own.
Damage from dry firing comes from over travel of the firing pin into the space that is normally occupied by the primer. This can damage the firing pin spring or the pin itself.