I am sure I am not the first to think of this. A rifled insert about six inches long, designed to fire a centerfire pistol cartridge in a shotgun chamber, would be an ideal device to suppress. The suppressor could be threaded onto the rifled insert and could extend to whatever length needed to reduce sound. A 12 gauge shotgun barrel is .724 to .729 inside, so the unit would have to be long and skinny. Shotgun barrels are 18 inches or longer to be legal. Most are 26-28 inches. With that much space it probably would not have to be very efficient to reduce the noise. Would the suppressor require an exterior shell, or could the shotgun barrel act as a shell? Does this concept have technical merit?

There are inserts available for shotguns. http://www.mcace.com/shotguninserts.htm I have thought about putting an insert into a break open single shot 12 gauge and filing the rest of the barrel with baffles. It would make a nice incognito suppressed rifle.

Ranb