12mm or 13mm cal., caseless, uses spin-stabilized rocket projectiles that accelerate to 1,250 FPS in .12 seconds, 2 in. (rare) or 5 in. barrel, 6 shot semi-auto action drives rocket projectile (primer activated) into fixed firing pin, smooth walnut grips, black, antique nickel, or gold-plated finish, 13 or 16 oz., "A" prefix until ser. no. 49, "B" prefixes followed, there are also other variations and experimental models in addition to the production models listed. Without rifling, this gun wasn't particularly accurate.
13mm cal., black, nickel, satin, or green finish, many variations with different grips, casings, and barrel lengths, wood cased, includes 10 dummy rounds and bronze medal honoring rocket pioneers Robert H. Goddard and Joseph J. Stubbs.