The only place you WILL see that is on facebook. They will not be producing it. Since is is larger than 50 cal, you have to show a "sporting" use for it- which is how shotguns and .600 Nitro Express rifles get around the ATF and "destructive Device". ATF ruled that failed the sporting use test, and would be a Class III firearm.
You want a hand cannon? sebu is making a 12 g pump PISTOL. Registers with the BATFE as an AOW, $5 tax.