Re: Big bore double pistol
Many of the old Howdahs were 20 bore or 16 bore. Any cartridge handgun today over .500 inch is considered a destructive device by the BATFE, if i recall correctly, so you'd be limited to a half inch bore howdah unless you wanted to pay the fees and jump through all the legal hoops.
Now, if you wanted to do that, just get a Class 3 manufacturer to take a 20 gauge side by side shotgun and cut it down, pistol grip it, and put threaded choke tubes in it. That would create a "Paradox"-style Howdah and you could shoot shotshells or cartridges through it. Magtech manufactures modern 20 gauge brass hulls that take pistol primers and a couple manufacturers offer molds for slugs. That would be a sweet pistola, for sure!
If you wanted to avoid the paperwork, just get a side by side rifle in 45-70 (Pedersoli makes a nice one) and have it chopped. Plenty of poop there.