Because ATF, at its whim, can and has declared certain semi-automatic* shotguns as destructive devices, even though they are mechanically no different than "sporting use" self-loading shotguns.
- JShirley
You are correct, but I blame Congress rather than the executive branch.
The law gives several definitions for "destructive device", one of which is anything above .50-caliber "except a shotgun or shotgun shell which the Secretary finds is generally recognized as particularly suitable for sporting purposes".
(Terrible grammar here by the way. "
Which" should come after a comma, and implies that a shotgun is recognized as suitable for sporting by definition! The New Deal hoplophobes who wrote that legislation obviously meant to say "except for a shotgun or shotgun shell
that the Secretary ...", but I doubt my nitpick would stand up in court.)
The point is, all gauge guns can be classified as destructive devices if the BATFE wants to. Most are not, so in a sense the BATFE is being pretty moderate. If they were truly pro-gun, they could classify all shotguns as legit, simply by putting the ordinary shooter's definition of "shotgun" (as opposed to "anti-tank rifle") into a reg. No one who has seen a
Lahti anti-tank rifle is going to mix it up with a 10-gauge goose gun, but they are both technically about 20mm in bore size. I'd say if it can properly function with non-metallic-hulled shells, it's a shotgun and not a DD ... but I'm not the ATF.
Funny that rifling never made an administrative difference here. ATR are obviously rifled and until a few decades ago, shotguns were smoothbore by definition. The ATF never put its foot down, probably because rifled shotguns are hunting weapons par excellence; fighting shotguns almost always smoothbore (though the SPAS-12, which caused so many to have a spaz in the 1980s, did IIRC have rifled tubes available).
Anyway, long story short, the problem was caused by Congress in 1934. I hope (and believe) the NRA and GOA look closely at appointees to BATFE, since they have the power to smash shotgun sales (except .410s) at the stroke of a pen.
* Also I'm not sure autoloading makes any difference here, under the law. Probably the BATFE is harder on semi-autos, purely out of prejudice, but they could be just as hard on single shots and manual repeaters. Isn't the M203 just a big shotgun anyway?