In Duncan Long's book The Complete AR15/M16 Sourcebook; What Every Shooter Needs To Know there is a section on the Bushmaster pistol/rifle.
According to the book, basically Colt started work in the late 1960s. It really wasn't termed a bullpup as it didn't have a stock and was more of an "arm" gun, which Colt described as a "lightweight rifle/submachine gun" for lack of a better term.
It was originally chambered for pistol ammunition but recoil was supposed to be so mild that rifle cartridges were soon adapted.
In 1969, it was tested by the Air Force for possible adoption as a survival weapon or as a 5.56mm submachine gun. No contracts were forthcoming though.
A slightly modified version did go into production via the commercial market. The new design was created by Mack Gwinn of Gwinn Arms and was sold as the Bushmaster pistol. The firearm utilized the basic conceop of the original but incorporated many more AR15 parts into ins design, keeping tooling costs down. BATF ruled it a pistol, hence the short barrel allowed on the firearm.
In the rush to get the first pistols to market, the original company suffered from poor product quality control and soon went bankrupt. In 1982 a new company was formed and the quality of its firearms was vastly improved.
A second model of the firearm brought the weapon full circle; a stock and a longer barrel were added and the pistol grip was moved into the conventional position. Since the internal parts were already mostly identical to the AR15, the end result was a version of the AR15 that had a stamped-steel receiver witha piston/recoil spring assembly over the barrel rather than a gas tube with a recoil/buffer assembly in the stock.
These firearms are quickly becoming collector's items. I haven't seen any at shows for several years now.
This company is the same company that now is one of the big players in the AR15 market.
Variations of this weapon were made in semi-auto and select-fire, in blued steel and nickel finishes and with wood stocks or folding metal stocks.
I've also seen information written up on the suppressed Ruger but can't recall where offhand. Perhaps in SAR?
If I remember where I saw it I'll post what I find.
