Quote Originally Posted by Irving View Post
.50 restrction is for rifled barrels I believe.
I would think this would be rifled. It really becomes a shotgun with a slug if not, which makes it much less impressive. I went back and found more. It apparently is a rifle. The justification is that

The inventor believes the rifle is not classified by the BATFE as a destructive because it is a sporting weapon. There is sporting weapons, such as shotguns and big bore double rifles, are exempt, the usual procedure it to obtain a letter from the BATFE stating that the particular weapon is a sporting weapon.
http://www.thefirearmblog.com/blog/2...ing-dinosaurs/

I don't know how much I or the BATFE will buy that logic but there it is.