I have caps in 9mm, 380acp, and 223 Rem. Next time you are at the range, have someone randomly pop one in a mag for you. Great way to train for misfires.
Great way to find out if you're flinching too.
The sights shouldn't move when the gun doesn't go bang.
Yes, but you don't even need snap caps for this. Load some magazines with empty casings randomly mixed in. Note: this only works with brass cases. If you shoot aluminum cases (CCI makes some) this will not work. linux is correct, this is a good failure drill. Put 5 to 7 empties in a mag (assuming 15 round mag).
Probably with most rifles. Not such a good idea with a semi-auto pistol unless you want to practice clearing jams. (OTOH, making it jam in practice sessions might be a good thing)
I had a 1911 that I used spent brass for snap-caps to dry-fire. After about 20 shots I had to switch brass before the firing pin penetrated the primer. When I stuck an empty in the magazine and dropped the slide, I only had a 3/4 chance of the brass chambering. I told the guy who bought it that it was 100% reliable IME feeding hardball, I didn't think to tell him it was not 100% reliable feeding empties.