Snap caps are snap caps. They're designed to "pad" the firing pin.
These may or may not be very close to the size of a real cartridge and aren't the same weight or balance.
If you want to cycle dummy rounds through the gun you need action proving dummies.
These are EXACT size, weigh, and balance dummy cartridges designed for testing the action.
http://www.brownells.com/.aspx/pid=4...-RIFLE-DUMMIES