The Bushmaster Arm pistol (also sometimes spelled as Bushmaster Armpistol) is an interesting weapon that appeared circa 1972. It was based on the IMP-221 Individual Multi-Purpose weapon, also referred to as GUU-4/P. The IMP-221 was conceived in 1968 as a compact personal defense weapon for US Air Force pilots. It was compact automatic weapon of bullpup, stock-less layout, firing .221 Fireball ammunition. After initial testing USAF rejected this project for being insufficiently accurate, but its basic concept was picked up by Mack Gwinn of Gwinn Firearms, USA.
Gwinn took the basic stock-less bullpup layout of IMP-221 and adapted it to slightly larger and more powerful .223 Rem ammunition, also using as much AR-15 / M16 components as possible to decrease product costs. Resulting weapon, designated as the “Bushmaster Arm pistol”, entered production in 1972. During early 1980s Gwinn Firearms changed its name to Bushmaster firearms, keeping its Armpistol in production until around 1988. Through these years, several slightly different versions were produced, which differed in safety arrangements, material of upper receiver and location of charging handle. A limited number of select-fire versions of Bushmaster Armpistol were made prior to 1986, while it was still legal in US to produce fully automatic weapons for civilian consumption.
The Bushmaster Arm pistol is intended to be fired from off-hand position, like a typical handgun. Since it has a bullpup layout with magazine behind the pistol grip, its grip is allowed to swivel around the barrel to the left or to the right for about 40 degrees. In firing position, pistol grip is held in more or less vertical position, and the receiver with gas tube and magazine housing is tilted sideways to clear the arm that holds the gun. Bushmaster Armpistol features gas operated action with long stroke gas piston and AR-15 style rotary bolt locking. Empty cartridges are ejected through the corresponding slots in the operating rod and in the top of the upper receiver. Early versions featured top-mounted charging handle, later production versions had it moved to the left side of the upper receiver. There were three versions of manual safety: earliest guns had safety lever above the trigger, on the left side of the trigger unit; subsequent versions had the safety switch mounted inside the trigger guard, in front of the trigger; and late production guns had AR-15 style safety behind the magazine housing, on the left side of the lower receiver. Ammunition was fed from M16 / AR-15 style box magazines. Fixed iron sights were allowed to swing sideways, corresponding to preferred firing position of the operator (left-hand or right-hand).
|Full text name||Gwinn Firearms Bushmaster Arm Pistol / Armpistol (USA)|
|Caliber cartridge||5.56x45 NATO, .223 Remington|
|Overall length, mm||524|
|Barrel length, mm||295|
|Weight loaded, kg||2.38|
|Magazine capacity, rounds||10, 20, 30|