the NFA gives the Attorney General to ban anything with a bore greater than 0.50" if he deems it lacks a "sporting purpose."
Right idea, wrong law. The 'sporting purpose" language doesn't show up in Federal law until the 1968 Gun Control Act. And, in that law, the authority is to ban imports, not US manufactured guns. Also, I believe that "anything with a bore over .50" applies to rifled bores.
Smooth bores (shotguns) are not in the same category. (example: a "sawed off" 12ga is not an NFA item because of its bore size (.72") but because of its barrel and/or over all length being below (shorter than) the minimum length listed in the law.)
Its easy to get confused.
The intention of any military small arms cartridge is to wound not kill.
Horsehocky!
That myth was advanced by the MacNamara defense dept. "whiz kids" as the justification for adopting the small bore 5.56mm round, along with the second part of the myth, that wounding an enemy takes 3 guys out of the fight, whereas killing him only removed one.
That is a "beancounter" analysis, makes for wonderful statistics, charts & graphs, but doesn't work evenly, or sometimes, even at all in the real world.
If you go back and read ALL that has been written about cartridge firearms since their invention, you will not find anything praising the wounding power of rounds, until you get to the 1960s. Just the opposite, in fact, one can find many examples of complaints about various rounds ONLY wounding and not killing, or not killing fast enough.
wounding one enemy doesn't automatically take 3 guys out of the fight. It may not even take the wounded guy out of the fight. It MIGHT, but accepting that it always does, as a given, is a foolish mistake.