Found one on google images.
that look just exactly what ryo would expect a mossberg bullpup to look like too neh. would be kewl thing if you could investigate more and post some stats and capabilities for the rest of us here neh ka
Type: Pump action shotgun
Gauge: 12, 20, or .410; Chamber 3" / 76 mm
Overall length: varies with different models
Barrel length(s): 355 - 500 mm (14" - 20") for combat/defensive versions. up to 711 mm / 28" in hunting versions
Magazine: 5, 7 or 8 rounds in underbarrel tube magazine
Mossberg model 500 shotguns were first introduced in 1961 by famous US-based gunmaking company O.F.Mossberg & Sons. In fact, one model designation covers a broad range of shotguns in four chamberings (12 gauge models 500A, 16 gauge - 500B, 20 gauge - 500C and .410 - 500D) and in a wide assortment of barrel and magazine lengths, finishes, stock shapes and materials. Other than hunting guns, Mossberg also offers a line of military / security / police guns under names of "Persuader" (various riot-type guns with fixed stocks, cylinder-bored barrels of short to medium length) or "Cruiser" (pistol-gripped shotguns originally intended for storage in police cruiser cars). In mid- or late eighties Mossberg also produced a short-lived bullpup version of the Model 500, with polymer stock, forward sliding pistol grip and additional automatic grip safety. For various reasons this conversion didn't lived on and was soon discontinued. Today Mossberg 500 shotguns are widely used by civilian shooters and hunters as hunting, self-defense and practice / sport guns; many Mossberg 500 guns are also in use by various Law Enforcement agencies in USA and abroad. Mossberg 500 shotguns also saw wide use by US Armed forces since about 1979, although today these are replaced in military service with improved Mossberg model 590 shotguns.
Mossberg model 500 shotguns are known for high reliability and durability, combined with affordable price. Some claim that those guns have loose construction which produces unnecessary noise when gun is cycled or shacked, but this feature in fact is intentionally built into the gun to provide maximum reliability under harsh conditions and heavy fouling.
Mossberg model 500 shotgun utilizes so called pump action, which is operated by sliding forend. Forend is connected with bolt group with dual action bars. Receiver is produced from lightweight aluminum alloy, and the bolt locks into the barrel extension using a single massive lug on the top of the vertically swinging locking piece, installed in the bolt body. Feed is from underbarrel tubular magazine, and one specific feature of Mossberg 500 shotguns is that cartridge lifter stays in raised position through most of the feeding cycle, ensuring trouble-free feeding of the cartridge into the barrel. Manual safety is conveniently located at the rear top of receiver (so called 'tang safety') and is easily accessible by either hand. Barrels are quick removable and could be replaced in less than a minute; there is a wide variety of barrels with fixed or removable chokes, ranging in length from 18.5 to 28 inches (470 to 711 mm); shorter barrels are available mostly for Law Enforcement or Military users. Standard furniture consists of a semi-pistol gripped stock and forend, made from wood or polymer. Pistol-gripped guns are known as 'Cruiser' shotguns, and recently Mossberg also added a line of Tactical models with retractable-adjustable (M4 carbine type) stocks and pistol grips.