Never dry-fire a rimfire,” my father commanded. “It will wear out the firing pin, and then I will wear you out.” Since then I’ve tested many theories, but never that one. (Perhaps I’m not as mad as I look!)
   Logically it makes sense: Since a rimfire’s firing pin strikes the steel breechface when dry-fired (rather than striking air like a centerfire or the soft brass of a cartridge), the firing pin or chamber rim could wear down. Many shooters believe this, but few can produce evidence of damage because most are afraid to dry-fire their beloved rimfires. Furthermore, manufacturer statements about dry-firing conflict because different brands of guns are made in different ways.
   So I want to know:
1 Will dry-firing damage rimfire guns?
2 If so, is the damage cosmetic and/or functional?
3 If so, how many dry-fires will hurt a gun?
4 If so, will all rimfires be damaged in the same way?

To determine if dry-firing damaged guns, the Mad Tester inspected chambers and firing pins under a microscope.

The Test:
   Using two new test guns, a Henry pump-action .22 rifle and a Browning Buck Mark II .22 pistol, I inspected each guns’ firing pin and chamber under a microscope. I recorded the surfaces of each via photography. Next I fired each gun 500 times, counting misfires and malfunctions. I inspected the chambers and firing pins for visible damage. Next I dry-fired each gun 500 times, and inspected. Then I dry-fired each gun another 500 times for a total of 1,000 dry-fires each, and inspected. Finally, the guns were fired 500 additional times apiece, noting misfires and malfunctions. Then I compared all data.

Conclusions
   In comparing before-and-after 1,000 dry-fire photos of the Henry’s chamber, slight marring of the breechface/barrel sleeve (where the firing pin strikes when dry-fired) was evident. The Browning’s chamber showed no marring from the firing pin, but showed slight wear from the extractor repeatedly striking the rim of the extractor slot. Neither gun’s firing pin exhibited visible damage. Indentations on fired cartridges from both guns were identical before and after dry-firing, indicating no functional damage. The Henry had two misfires out of 500 shots before dry-firing, and one misfire out of 500 shots after dry-firing. The Browning had no misfires before or after dry-firing; thus, I conclude no functional damage was incurred on either gun after dry-firing 1,000 times.

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