It was forced to be a DD by name, like the drum fed shotguns.
Any self loading shotgun can be converted to full auto, except that the SPAS and the Streetsweeper suffer from "Evil black rifle" syndrome. Here's the deal: any firearm over .50 caliber INCLUDING Shotguns, deed a "sporting use" exemption for them to be sold without a destructive device permit. The power's that be decided that the SPAS and the Streetsweeper were not "sporting firearms", and thus were not exempt(which is complete and utter bull**** - if you're regulating by caliber, it should be the CARTRIDGE that determines whether or not it can be sold - uses regular 12 gauge 2 3/4? Then it should be legal).
The reason I brought it up is because I was recently doing research on DD's for a 4 bore project(which is way, waaaay over .50
), just not in the way most people use them - mini arty. I wanted to know what I had to do to avoid the DD paperwork(which I couldn't get here in New York anyway), and make sure it was registered as "sporting firearm"