The development of small arms is a long and complex process that requires collaboration between engineers and designers as well as military strategists. The process is not purely about developing powerful weapons, instead it is about creating weapons that meet certain needs or parameters for the battlefield. (These are the future military guns of the world.)
As the preeminent military power on the planet, the U.S. military is constantly in the process of developing weapons and over the years it has produced many prototypes. Some of these prototypes went on to see widespread use throughout the military while there are others that did not make the cut.
Here 24/7 Wall St. is taking a look at some of these experimental weapons that did not make the cut. To identify prototype small arms not approved for the U.S. military, 24/7 Wall St. reviewed experimental infantry arms cataloged by Military Factory, an online database of military vehicles, aircraft, and arms. 46 prototypes did not pass muster; 25 of these were American-made. We have ranked 17 of these America-made weapons according to when the prototype was first tested. Supplemental data on the type of weapon, maximum effective range, manufacturer, or the caliber and feed used by each gun also came from Military Factory.
One example of these experimental weapons is the Barrett XM109 OSW, which expands on the Barrett M82/M107 anti-materiel rifle family. This gun basically combines a sniper rifle with a grenade launcher and is chambered to fire 25x59mm smart grenades. While the body style and range of this weapon are akin to that of traditional sniper rifles, this weapon is designed to destroy whatever it hits. The smart grenade ammunition is also capable of featuring variable warhead loads for different combat scenarios. The XM109 was reportedly folded into a larger anti-materiel rifle program in 2006. (These are the US military’s 20 heaviest guns.)
It is worth noting that these prototypes and experimental weapons on this list had mixed results in terms of implementation, sometimes inspiring a later, more successful model, and other times failing.
Here is a look at the prototype guns not approved for widespread use in the U.S. military:
17. Stoner 63 (Universal Combat Weapon)
- First year of prototype trials: 1963
- Type: Modular assault weapon
- Maximum effective range: 1,800 ft.
- Caliber and feed: 5.56x45mm NATO; 30-round detachable box magazine
- Manufacturer: Cadillac Gage Company
16. Colt XM148 UBGL
- First year of prototype trials: 1966
- Type: Under-barrel grenade launcher
- Maximum effective range: 800 ft.
- Caliber and feed: 40x46mm; Single-shot
- Manufacturer: Colt Firearms
15. Aerojet XM174
- First year of prototype trials: 1968
- Type: 40mm automatic grenade launcher
- Maximum effective range: 1,150 ft.
- Caliber and feed: 40x46mm; 12-round detachable drum magazine
- Manufacturer: Aerojet Ordnance Manufacturing Company
14. China Lake Grenade Launcher
- First year of prototype trials: 1968
- Type: 40mm pump-action grenade launcher
- Maximum effective range: 1,150 ft.
- Caliber and feed: 40x46mm; 3-round tubular magazine
- Manufacturer: China Lake Naval Weapons Center
13. AAI Inline Machine Gun (IMG)
- First year of prototype trials: 1970
- Type: Multi-shot weapon system
- Maximum effective range: 3,280 ft.
- Caliber and feed: 7.62x51mm NATO; 100-round disintegrating link-belts
- Manufacturer: AAI Corporation
12. Bushmaster Arm Pistol
- First year of prototype trials: 1977
- Type: Bullpup personal defense weapon
- Maximum effective range: 325 ft.
- Caliber and feed: 5.56x45mm NATO; 20-round detachable box magazine
- Manufacturer: Bushmaster Firearms
11. Heckler & Koch HK CAWS
- First year of prototype trials: 1983
- Type: Select-fire automatic combat shotgun
- Maximum effective range: 500 ft.
- Caliber and feed: 12-gauge; 10-round detachable box magazine
- Manufacturer: Heckler & Koch
10. AAI CAWS (Close Assault Weapon System)
- First year of prototype trials: 1985
- Type: Assault shotgun
- Maximum effective range: 500 ft.
- Caliber and feed: 12-gauge; 12-round detachable box magazine
- Manufacturer: AAI Corporation
9. Ares Defense FMG (Folding Machine Gun)
- First year of prototype trials: 1986
- Type: Compact submachine gun
- Maximum effective range: 250 ft.
- Caliber and feed: 9x19mm Parabellum; 20- or 32-round detachable straight box magazine
- Manufacturer: Ares Defense Systems
8. Pancor Jackhammer
- First year of prototype trials: 1987
- Type: Automatic shotgun
- Maximum effective range: 500 ft.
- Caliber and feed: 12-gauge; 10-round cassette
- Manufacturer: Pancor Corporation
7. AAI ACR (Advanced Combat Rifle)
- First year of prototype trials: 1989
- Type: Assault weapon
- Maximum effective range: 2,000 ft.
- Caliber and feed: 5.56x45mm Flechette; 30-round detachable box magazine
- Manufacturer: AAI Corporation
6. Colt ACR (Advanced Combat Rifle)
- First year of prototype trials: 1989
- Type: Assault weapon
- Maximum effective range: 1,800 ft.
- Caliber and feed: 5.56x45mm NATO; 30-round detachable box magazine
- Manufacturer: Colt Firearms
5. Heckler & Koch HK XM29 OICW
- First year of prototype trials: 1995
- Type: Combination assault rifle
- Maximum effective range: 3,280 ft.
- Caliber and feed: 5.56x45mm / 20x85mm; 20- or 30-round detachable box magazine / 5-round detachable grenade box
- Manufacturer: Heckler & Koch
4. General Dynamics XM307 (ACSW) Advanced Crew-Served Weapon
- First year of prototype trials: 2004
- Type: Automatic grenade launcher
- Maximum effective range: 6,560 ft.
- Caliber and feed: 25x39mm; 31-round ammunition drum or belt-fed
- Manufacturer: General Dynamics
3. General Dynamics XM312
- First year of prototype trials: 2004
- Type: Heavy machine gun
- Maximum effective range: 6,560 ft.
- Caliber and feed: .50 BMG; 200-round belt
- Manufacturer: General Dynamics
2. General Dynamics XM806 (LW50MG)
- First year of prototype trials: 2009
- Type: Heavy machine gun
- Maximum effective range: 6,560 ft.
- Caliber and feed: .50 BMG; 265-round belt
- Manufacturer: General Dynamics
1. Barrett XM109 OSW (Objective Sniper Weapon)
- First year of prototype trials: 2014
- Type: Anti-material grenade launcher / rifle system
- Maximum effective range: 6,335 ft.
- Caliber and feed: 25x59mm; 5-round detachable box magazine
- Manufacturer: Barrett Firearms Manufacturing
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