IT SOUNDS like a make-believe movie monster or something from Doctor Who, but it's not.

Imagine a 50kg shotgun with a single barrel more than 2m long and a bore diameter of 3.8cm. Its hinged breech takes a huge brass cartridge case, charged with 680 grams (1.5 pounds) of shot and 85 grams (3 ounces) of powder. Instead of the normal buttstock, it has a wooden handle.

Being designed for swivel-mounting on a purpose-built, flat-bottomed boat, this ballistic behemoth is known as a punt gun. Such guns were popular among English and Irish wildfowlers who stalked ducks and geese on estuaries and coastal marshes more than a century ago, and some remained in use until recently.

But early versions of the boat-borne brutes go back more than 400 years. An English flintlock piece from the 1680s is in the collection of Mike Townsend, a punt gun user from Essex in England. Amazingly, this ancient gun was still in service just 10 years ago.

Double-barrelled punt guns were "too heavy and cumbrous", according to the famous British gunsmith and historian, W.W. Greener, but first-quality specimens were occasionally made.

The renowned Colonel Peter Hawker had one with percussion ignition on one side, flintlock on the other. Because percussion ignition is faster, a single pull of the lanyard discharged both barrels with the flintlock barrel igniting a split second later, thus providing a fast follow-up.

Some of a British punt gun's massive recoil was absorbed by ropes or India-rubber buffers, the rest by the combined weight of the gun, the hunter and the punt, aided by water drag.

Punt guns were never popular in the US, and most states banned them in the 1860s. Surviving examples all seem to be crudely made muzzleloaders.

Usually, Americans made no attempt to mount a punt gun on the boat. According to Bob Hinman, in his book The Golden Age of Shotgunning, recoil was "taken on the shoulder by a mass of dried seaweed serving to soften the blow".

Nothing stopped the gun from bucking mightily. I take this to mean American punt gunners were either impervious to pain or supremely stupid.

American market hunters preferred to use home-made battery guns on their boats. In Hinman's words, these resembled organ pipes, with as many as 10 six gauge to 12 gauge barrels, usually recycled from old guns, welded together and set to cover a wide area. They were ignited almost simultaneously by an open-air powder train. Ye gods.

In Australia, regulations would make punt guns and battery guns illegal, and our shooters never took to punt guns.

To today's duck hunters, the idea of punt gunning is repulsive. Sneaking up on ducks and shooting them on the water is a big no-no in Australia.