A blunderbuss (roughly translated thunder pipe) was a short muzzle loading firearm of enormous bore diameter and short barrel length typified by a trumpet shaped muzzle. Some had stocks like a traditional musket, some were stockless like a large pistol and some had just a nub of a stock suitable only for tucking it under your arm. These were porously designed for use in close quarter combat aboard ships and by carriage drivers in defense against highwaymen.
The blunderbuss is all but forgotten. Practically nobody collects them. They abound in myth and misunderstanding. For example, they were not loaded with nails and broken glass (except by idiots) but with precisely measured amounts of powder and shot. The trumpet shape of the muzzle was not designed to spread the shot (which is impossible) but rather to act as a funnel to facilitate faster loading. The few that I have handled were all flintlocks and all had a bore diameter of around an inch and a quarter to an inch and a half, 125 to 150 caliber! Such a barrel could fire nine .45 caliber balls in one shot.
The closest thing we have now to the blunderbuss is the Mossberg Shockwave and the Remington Tac 14. These serve the same purpose. Even though they are of significantly smaller bore diameter, they hold multiple high velocity shells and unlike their flintlock predecessors, they don't malfunction approximately one out of seven shots.
Even though these short "firearms" are one of the hottest fads going, I don't think most buyers have the slightest idea how effective these short shotguns can be in confined spaces where you just can't have a full stocked shotgun such as inside the interior of your car, or packing it inside of a suitcase to get past the front desk of a motel without alarming the desk clerk.
I for one thought that they were gimmicks when they first came out but after using one I am totally sold. The point is that they are not the best shotgun that you can have, but they are the generally the ONLY shotgun that you can actually have with you.
Contrary opinions are certainly welcome.