The AR-10 is an automatic rifle which fires 7.62 × 51 mm NATO ammunition. Designed by Eugene Stoner at ArmaLite, the AR-10 was not widely used and perhaps 10,000 examples were built. Nevertheless it is historically notable as being the basis for the later AR-15, which was adopted by the US Army as the M16. Recently, the Armalite trademark was bought and a new rifle, resembling the old Armalite AR-10, was introduced.

ArmaLite first opened as a division of Fairchild in 1954, specifically to bring new materials and designs to the firearm industry. They quickly released a number of interesting designs. Later that year they were joined by Eugene Stoner, who started looking for new projects.

At the time the Army was in the midst of testing several rifles to replace the obsolescent M1 Garand. Springfield Armory's T44E4 and heavier T44E5 were essentially cleaned up versions of the Garand chambered for the new 7.62 mm round, while Fabrique Nationale submitted their FN FAL as the T48. Armalite entered competition, even though they were late in testing at that point, and started work on what would become the AR-10.

While mostly original, the AR-10 borrowed features from other designs. From the FAL it took the hinged receiver, which allowed the rifle to be "folded open" for cleaning like a break-action shotgun. From the Johnson M1941 Rifle it borrowed the bolt locking mechanism. From the German FG42 and Johnson Light Machinegun came straight-line recoil and high-mounted sights. The use of plastics, titanium, and aluminum were common in the aircraft industry though they had yet to make it into firearms.

Most gas-operated rifles divert combustion gas a short distance from a port in the barrel to a chamber to operate the action. In Stoner's design, the gas travels from a port at the top and middle of the barrel through a metal tube approximately 30 cm into a chamber formed between the rear of the bolt and the inside of the bolt carrier. This utilization of the bolt and bolt carrier for the separate actions of a piston and gas cylinder simplifies construction. The result was less weight in the operating mechanism and the isolated movement of the bolt carrier in line with the bore and the shooters shoulder. The receiver itself was made from machined aluminum, dramatically reducing weight. The bolt locked into an extension on the barrel instead of the receiver allow for a lightweight receiver while not sacraficing strength in the bolt locking mechanism. To further reduce weight, the barrel was made of a stainless steel liner swaged inside an aluminium barrel. The stock was made from a plastic-reinforced fiberglass with a core of rigid plastic foam.

The most noticeable difference in the AR-10 design was its layout. Traditional rifle design placed the barrel in line with the shooter's eye, with sights mounted on top. In order to transfer the recoil to the shoulder, the stock bent down behind the receiver, and was also used as the rear hand grip. However this led to serious recoil problems, since the barrel is above the support point on the shoulder, every shot forces the barrel to rise.

For the AR-10, Stoner placed the barrel in-line with the stock, thereby reducing the climbing action. However this placed the shooter's eye well above the barrel, where the sights are normally mounted. He solved this problem by simply moving the sights upward, mounting them on a rail that also served as a convenient carrying handle. The charging lever was mounted under the handle, in the form of an upside-down trigger. All of the "furniture" was made of a brown fiberglass, another innovation that reduced weight.

The differences between AR-10 and other rifles of the time were stark, and its appearance was unique. When it was introduced in 1955, it was almost two pounds (1 kg) lighter, easier to control in automatic fire, and was handled better than any other weapon of the period. The composite barrel proved to not be strong enough for torture tests conducted by the United States Army. Armalite replaced it with a conventional chromium-molybdenum-vanadium steel alloy, but the Army rejected the design. Army politics are credited with rejection of both the AR-10 and T48 (FN FAL). It was clear that both of these designs were superior but they suffered from not having been developed by the Springfield Armory. In the end the Army chose the conventional T44, which entered production as the M14 rifle in 1957.

A manufacturing license was sold to a Dutch company named Artillerie Inrichtingen. Production was limited, with only Sudan and Portugal purchasing AR-10 rifles for their militaries. Production of the AR-10 ceased during the early or mid-1960s and only around six thousand military AR-10's being made, and some additional number in semi-automatic mode for civilian use. When the M16 was adopted as the standard US rifle, the AR-10 gained cult status and became a coveted collectors item.

ArmaLite also started a program to produce "low cost" rifles in 5.56 mm and 7.62 mm as the manufacture of their AR-10 and AR-15 rifles had been licensed already. These rifles utilized more traditional gas pistons along with stamped and welded steel construction in place of aluminum forgings. Known as the AR-16 and AR-18 respectively, the former was produced only in prototype quantities after the M16 was adopted, and the AR-18 saw only limited production.

In 1995 Eagle Arms purchased the ArmaLite brand name and re-introduced the AR-10 to the market. With the original brown plastic it is known as the AR-10A, and with M16A2-style furnature it becomes the AR-10A2 while the AR-10A4 has the "flat-top" style receiver with the Picatinny rail instead of the carrying handle, and the AT-10(T) is a match-grade version of the A4.

AR-10 Ultra

In October of 2003, Armalite began offering the AR-10 (T) Ultra, chambered in 300 RSUM.

A tech note released by Armalite in January of 2006 mentions some problems associated with adapting the significantly more powerful round to the AR-10 platform:

"The .300 RSUM cartridge is much wider than the 7.62mm cartridge for which the AR-10(T) (sic). This forces the bullet tip low and in towards the centerline of the magazine. It makes feeding far more difficult, and some loss of reliability compared to the AR-10 is to be expected. In addition, the larger diameter cartridge cases are forced into a tight, tall stack in the magazine. Each round loaded resists insertion more than the last. A magazine that holds 10 7.62mm rounds will hold 5 .300 RSUM cartridges. Higher capacity magazines are not practical. Great care must be taken when loading the magazine for the AR-10(T) Ultra. Simply pushing the cartridges into the magazine will likely result in miss-feeds. Once the cartridges are in the magazine, it is necessary to push up and down on the top of the stack to remove any binding that resulted in loading. A tell tail sign that there is binding on the stack, is that the magazine will not fully engage the magazine catch if the bolt is closed or excessive force is required to insert the magazine."

External links

• Buddy Hinton Collection / AR10
• Firing the AR10
• Armalite home page