WILL NOT FIT IN 37mm. MUST BE 40mm NFA REGISTERED DESTRUCTIVE DEVICE. Beehive Round. These Are Rifled Barrels, Not To Be Confused With Other Cheaper Version Of This Unit. You Load The 22lr Rounds In The Chambers, And Insert A Large Pistol Primer In The Back. Wham! You're In Business! Also comes with mini ramrod to remove spent casings. You can use this in your registered 40MM 203 style launcher or your M79 should fire launcher also.
IMPORTANT: ONLY USE A LARGE PISTOL PRIMER, NOT A MAGNUM PRIMER!