Howdy
Everybody always says not to dry fire a 22 rimfire revolver. (Well, almost everybody anyway)
Study this photo, showing where the firing pin hits a rimfire round in my Model 617.
Notice there is plenty of clearance with the counterbore for cartridge rim. The firing pin will not strike the cylinder.
Although generally I do not like to dry fire firearms, doing so a few times will not hurt a Model 617.
Regarding using spent rimfire cartridges, as snap caps, I
do not recommend that.
The purpose of a snap cap is to cushion the firing pin as it strikes a primer. If you are going to use spent rimfire brass, be sure to rotate the brass each time so the firing pin is not striking the same spot. Once a rimfire rim has been struck a couple of times, it will no longer provide any cushioning for the firing pin. The pin will fall all the way and the brass will have been reformed and will provide no cushioning at all.
The same with wall anchors. Rotate them so the firing pin is not striking the same place over and over again.
A few more photos:
My S&W Model 17-3 from 1975
A K-22 Masterpiece from 1950
A K-22 Outdoorsman from 1932. Notice over the years it has been dryfired out of battery quite a lot, by all the firing pin hits on the rear face of the cylinder. This revolver happens to be the most accurate 22 I own. I have no idea if the firing pin has been replaced over the years, but you can see that when in battery the firing pin does not strike the edge of the chamber counterbore. Not as much clearance as in the newer ones, but the firing pin does not strike the rear of the cylinder.