(2) Any weapon by whatever name known which will, or which may be readily converted to, expel a projectile by the action of an explosive or other propellant, the barrel or barrels of which have a bore of more than one-half inch in diameter (.50 inches or 12.7mm), except a shotgun or shotgun shell which the Secretary[clarification needed] finds is generally recognized as particularly suitable for sporting purposes;
A large bore machinegun such as the Oerlikon on that worse than useless show will transfer as a machinegun. Nothing trumps anything else...they are what they are. According to friends in ATF the gun will be listed in the registry as an MG/DD but it will transfer just like your AC556 so you can legally own it in Indiana and it will transfer through a regular class 2 or 3. You don't need a DD Dealer/Mfg to do the transfer. There are a number of large bore MG's out there. I've fired a few of them myself and have friends who own or have owned them. None of them were DD dealers and all transferred as MG's.
MG 151/20 is a Mauser 20mm belt fed MG. A friend had a couple of them and they were really cool. Look them up on google and maybe on youtube. I think my buddies guns are in some vids there. There is also a 40mm Bofors that the idiot from FPS russia did some vids with. That one is an MG as well....belonged to a friend. I know of a number of guys who have Oerlikons or Hispano-Suiza guns in 20mm. I have some DD's that aren't MG's but that doesn't really relate...they are DD's.
Frank
Though they may transfer as MG's, are they still 2-stamp guns?