Actually, the practice of not dry firing a 22 is the traditional thing to do but from a modern design point of view, not all ways true. For instance, The Ruger 10/22 design will handle moderate amounts of dry firing along with the Ruger MK series of pistols. The firing pin designs of today have rather large strike bottom out features that ensure the firing pin tip does not exceed the majority of the rim head space when fully extended. The problem in a modern design comes from crystalizing the firing pin with "excessive" dry firings and in some cases, dimpling the chamber face could happen with over use of dry firing a rim fire gun. Even some designs that may be like a new-ish Marlin 39 should not be dry fired simply because its in fact an old design and those pins are not robustly designed in the first place. So if you want to be non technical, Don't dry fire RF guns..... but some designs can handle moderate amounts just fine.