From Internet Movie Firearms Database - Guns in Movies, TV and Video Games

Pre-production Pancor Jackhammer - proprietary 12 gauge

Last remaining prototype Pancor Jackhammer - standard 12 gauge. Note MP5SD handguard.

The Jackhammer is a bullpup automatic shotgun which never entered production, using a revolver-style detachable cylinder (referred to as a "cassette") with a rotating action similar to the British Webley-Fosbery Automatic Revolver, and a gas-seal system similar to that of the Nagant Revolver, though with the barrel moving back to form the seal instead of the cylinder moving forward. A forward-back pump-action forend is used to cock the weapon initially, after which it indexes automatically. The mechanism is indexed by a cam on an operating rod attached to the barrel, which moves in a zig-zag groove to rotate the cylinder to the next chamber with each forward-back motion. The barrel is blown forward by gas tapped from the bore and returned under spring pressure.

It is often seen in videogames as a "super shotgun;" the Jackhammer's popularity is due, in large part, to the futuristic look of the weapon, and sometimes mistakenly described as the only fully automatic shotgun in existence. There is an element of unreality in featuring the Jackhammer in any context, as the weapon never made it past prototype stage; only two guns capable of firing in fully automatic mode were ever made. The real guns had problems with cassette grooves needing to be manufactured to extremely tight tolerances for the weapon to cycle correctly; typically, the full-auto guns could only manage two or three shots sequentially before failing to cycle. The weapon's design was also cumbersome and uncomfortable to shoot, and the factory-sealed ammunition cassettes of the final version could not be reloaded in the field. A well-known fact is that more Jackhammers have appeared in any given work of fiction than ever existed in real life.

One unique feature was that the ammunition cassette could be combined with an additional assembly containing an array of strikers and a pressure plate to turn it into an ersatz landmine, referred to as the "bear trap." The precise utility of this is debatable since the plate was almost as large as another cassette and the "mine" would expend ten rounds to kill one person, even if it was guaranteed someone would actually stand on it.

Two pre-production weapons were subject to full destructive testing, and just one functional Jackhammer remains in existence, a heavy toolroom prototype with a cylinder which accepts standard 12-gauge shells. This is not the final version, and among other things requires that the weapon be almost completely dismantled in order to reload it. For a time this weapon was owned by designer John Anderson; it was later sold to a movie armourer and fitted with the handguard grip of an MP5SD since the original smooth forend was thought to be too slick to reliably operate. The weapon is currently registered to a collector in New York.

The Pancor Jackhammer can be seen in the following video games:

Specifications

(Designed in 1984 and patented 1987, never produced)

Type: Shotgun

Caliber: 12 gauge preloaded (production), standard 12 gauge (prototype)

Weight: 10.1 lbs (4.57 kg), about 14 pounds for toolroom prototype

Length: 31 in (78.7 cm)

Barrel length: 20.7 in (52.5 cm)

Capacity: 10-Round preloaded ammunition cassette (production), 10-round revolver cylinder (prototype)

Fire Modes: Semi / Full-Auto