Which snap cap works the best for a Mossberg 500. Read some get stuck in chamber
29sf, Welcome to the forum! Why do you want a snap cap for the 12Ga? Are you running a special type of drill? (stoppages, from misfire) ??? Are you worried about dry fire? (nothing to worry over) ::)
I used them in training for loading and working the gun for new shooters.... nice to know they can handle the gun before live rounds are introduced.
Company called A-ZOOM 12ga ( aluminum ) about $10
Works 100% in maverick 88 ( poor mans 500 )
http://www.amazon.com/A-Zoom-Precision-Snap-Caps-Gauge/dp/B0029M2YWE/ref=sr_1_3?ie=UTF8&qid=1405604293&sr=8-3&keywords=a+zoom+snap+cap
Brownells sell very nice "Dummy" Rounds for just about anything you'll have
Here's the 12g Dummies:
http://www.brownells.com/gunsmith-tools-supplies/general-gunsmith-tools/cartridge-dummies/12-ga-shotgun-dummy-rounds-prod67708.aspx