Snap Caps, for what it's worth - I've got a 1902 Webley falling block in 375 X 2½ which I don't like storing cocked. I decided to make a simple snap cap by sawing off a case (sawn off to about 1" because I didn't want it to ever be confused with a live cartridge) and using the primer seating stem on my press to force a piece of resilient plastic into the primer pocket. Because I didn't want to sacrifice an expensive 375 case I used a 303 British case which has almost the same head dimensions. Being a frugal sort of lad I use the cut off end of plastic wall plugs for the cushion. When it gets a bit battered I just decap the case and ram a new one in.