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6×45mm SAW
Type Rifle
Place of origin Flag of the United States.svg United States
Production history
Designer Frankford Arsenal
Designed Early 1970s
Bullet diameter 6.17 mm (0.243 in)
Neck diameter 6.63 mm (0.261 in)
Shoulder diameter 9.72 mm (0.383 in)
Base diameter 10.26 mm (0.404 in)
Rim diameter 10.36 mm (0.408 in)
Case length 45.01 mm (1.772 in)
Overall length 65.54 mm (2.580 in)
Primer type Boxer

The 6×45mm SAW describes an experimental series of rimless bottlenecked intermediate cartridges developed in the 1970s for the U.S. Army. The cartridges were produced in a variety of sizes and from a variety of materials. The intent was to develop a cartridge that would replace all 5.56×45mm NATO weapons as well as most 7.62×51mm NATO rifles and machine guns in the U.S. military. Eventually, the 5.56mm was retained and only the machine gun portion of the SAW (Squad Automatic Weapon) competition was successful. That program led to the M249 light machine gun.

Note that the dimensions listed to the right are for 6×45mm SAW rounds.[1] Three versions were produced for testing in the early 1970s. An aluminum-cased version was developed, as well as the 6mm SAW Long which was slightly longer (by about 5 mm).[2]

Design and developmentEdit

During the 1970s, the U.S. Army was looking to develop a new squad automatic weapon (SAW) that was lighter than the M60 machine gun with an effective range out to 800 m. The 7.62 mm cartridge was too heavy and the 5.56 mm cartridge could not provide effective performance at that range. Research led to the development of the 6×45mm SAW cartridge. Its 105 gr (6.8 g) bullet had a muzzle velocity of 2,520 feet per second (770 m/s) and muzzle energy of 1,488 ft·lb (2,017 J). The relatively heavy bullet combined with a moderate velocity had optimum long-range performance. A light-alloy cased version of the round was also produced. Because aluminium alloy had a tendency to catch fire, the case length was extended to 50 mm (2.0 in) to make up for loss in capacity caused by the need to line the inside of the case with fire-resistant material. Although the 6mm SAW's performance proved satisfactory, there were supply concerns over adopting a third rifle caliber. Development of the 6mm SAW was abandoned when an improved 5.56 mm round was promised, which arrived as the M855.[3][4][5][6][7][8] 6×45mm SAW cartridges depending on their case materiel and bullet weigh 10.6 to 15 grams (164 to 231 gr).

Chambered FirearmsEdit

See alsoEdit


  1. on the 6x45mm SAW (translated)
  2. on the 6x50mm SAW Long (translated)
  3. The Case for a General-Purpose Rifle and Machine Gun Cartridge (GPC) by Anthony G Williams Archived 2014-11-09 at the Wayback Machine.
  5. THE .256 INCH BRITISH: A LOST OPPORTUNITY by Anthony G Williams

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