It is unprobable that you find such, most snap-caps cartridges are made for combination shotgun or drillings which have a fine firing-pin(such as the lead in a lead pencil) which upon hitting receiver will gradualy crystalise and break. Another no-no is dry firing a rim-fired weapon since this will leave indentations in the firing chamber and cause: bad headspace, mis-fires, and what not.
As in the case of a bolt action rifle the firing-pin is massive enough that it will never break for this type of reason, thus you can dry-fire at will.
Since the 7mm Rem. Mag. is seldom seen in combo-shotguns & drilling, then I'm assuming that you have a bolt-action rifle.
