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Bushmaster Arm Pistol

Bullpup Personal Defense Weapon (PDW)

Untied States | 1977

"Not quite pistol, not quite carbine - the limited-run Bushmaster Arm Pistol was born from an original USAF Vietnam War-era prototype design that went nowhere."

Authored By: Staff Writer | Last Edited: 08/18/2023 | Content ©www.MilitaryFactory.com | The following text is exclusive to this site; No A.I. was used in the generation of this content.
The Bushmaster "Armpistol" (or "Arm Pistol") is rooted in a United States Air Force (USAF) trials program seeking a "Personal Defense Weapon" (PDW) for standard issuance to downed airmen in a combat zone. At this point in American history, the Vietnam War (1955-1975) raged in Southeast Asia so there grew a concerted effort to arm such personnel in the event of their aircraft being shot down Behind Enemy Lines. The program produced prototypes - these carrying the designation of "IMP-221" (IMP = "Individual Multi-Purpose weapon") and known in the USAF inventory as the "GUU-4/P" - but was ultimately not furthered nor adopted. The gun was eventually brought to the civilian market by Gwinn Firearms / Bushmaster before its story ended in the late-1980s.

The original USAF specification of the late-1960s called for a weapon to feature an overall length no more than 13 inches, weighing a handy 1.5 lb or less, and able to reach out to targets at 100 meters - in essence a very portable sidearm with greater capability than a standard service pistol though not quite as bulky and complex as a battle rifle / assault rifle. The design was arranged in a "bullpup" fashion meaning the internal action and feeding mechanism were set aft of the trigger / pistol grip section. This arrangement allowed gun-makers to fashion infantry-level solutions shorter in overall length than typical long-gun counterparts where the feed and action are set ahead of the trigger / pistol grip. For the IMP-221 this proved something of a necessity to stay within the restrictions imposed by the USAF requirements. The barrel assembly measured 11 inches long and overall length became 20.6 inches for the completed product. Weight reached 6.25lb.

Beyond its relatively compact dimensions, the gun was fully ambidextrous from the get-go and the rear section of the receiver was designed to "pivot", or twist, left or right apart from the forward. This feature allowed the shooter to "rest" the gun along either forearm as no conventional shoulder support / stock component for this short-barreled weapon could be fitted. The gun was chambered for .221 "Fireball" (5.56x36mm "Wildcat"), a slightly shorter cartridge when compared tothe standard NATO 5.56x45mm offering. Internally, a rotating bolt-action system was in play (as in the AR-15 / Colt M16's function), this coupled to a long-strike gas-operated system (akin to the famous Soviet / Russian Kalashnikov series of infantry assault weapons - namely the Ak-47). Some AR-15 parts (including the rotating bolt) were utilized in the IMP-221's makeup.

In the end, the IMP-221 was not an outright success for the USAF with trials of the prototypes having been had at the USAF Armament Laboratory (Elgin Air Force Base). The gun was not a vast improvement over current market solutions available to the service and there were revealed inherent issues in the overall arrangement and function of the weapon - particularly the sights coupled with the pivoting action and short length of the weapon. The bullpup nature also brought the fiery action and ejection closer to the face - a common issue of even modern bullpup designs.

Former SPECOPS player Mack Gwinn, Jr later acquired the rights to the weapon and reimagined it for the consumer market as the "Arm Pistol" under the Gwinn Firearms (of Bangor, Maine) brand label, this version now chambered in 5.56x45mm firing from a M16-style detachable box magazine. This form eventually ended in the hands of Bushmaster Firearms and the civilian market model went on to see limited sales between 1977 and 1988.

A version of the Bushmaster Armpistol is on full display in the extensive arms section of the USAF Armament Museum in Florida.

Content ©MilitaryFactory.com; No Reproduction Permitted.
The physical qualities of the Bushmaster Arm Pistol. Information presented is strictly for general reference and should not be misconstrued as useful for hardware restoration or operation.
510 mm
20.08 in
O/A Length
290 mm
11.42 in
Barrel Length
4.30 lb
1.95 kg
Gas-Operated, Rotating Bolt; Long-Stroke Gas Piston
5.56x45mm NATO
20-round detachable box magazine.
Iron Front and Rear.
Performance specifications presented assume optimal operating conditions for the Bushmaster Arm Pistol. Information presented is strictly for general reference and should not be misconstrued as useful for hardware restoration or operation.
325 ft
99.1 m | 108.3 yds
Notable series variants as part of the Bushmaster Arm Pistol Bullpup Personal Defense Weapon (PDW) family line.
Arm Pistol / Armpistol - Base Series Name.
Global customers who have evaluated and/or operated the Bushmaster Arm Pistol. Nations are displayed by flag, each linked to their respective national small arms listing.

Contractor(s): Gwinn Firearms (Bangor, Maine) - USA / Bushmaster Firearms - USA
National flag of the United States

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Image of the Bushmaster Arm Pistol
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Design Qualities
Some designs are single-minded in their approach while others offer a more versatile solution to requirements.
Some designs stand the test of time while others are doomed to never advance beyond the drawing board; let history be their judge.
Developments of similar form-and-function, or related, to the Bushmaster Arm Pistol Bullpup Personal Defense Weapon (PDW).
Going Further...
The Bushmaster Arm Pistol Bullpup Personal Defense Weapon (PDW) appears in the following collections:
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