I wonder about that "all 22 rifles" comment. I do not know that it is wrong; I do know that my Anschutz requires "dry fire device" for that practice.All 22 rifles are safe to dry fire, when working as designed and does not have worn parts. I collect Mossbergs (not noted for being expensive rifles) some from back in the 30's. Have been shooting many different brands since the 1950's and have NEVER had a chamber face hit by fire pin! They are NOT designed "to impact the rim"! If they were the manufactures would be repairing thousands of guns every year! Serious target shooters dry fire for practice hundreds of time a month, if not more!
I inadvertently peened the chamber face on my Ruger MK.II when, after cleaning, the firing pin stop fell out and I did not notice until after the gun was reassembled and dry fired. Fortunately, there is a very effective tool for repairing the dent.
Pete