Old Version of AR-10

 AR-10

Caliber: 7.62×51mm NATO

The AR-10 is a semi-automatic rifle that fires the 7.62×51mm NATO standard cartridge. Designed by Eugene Stoner at Armalite, the AR-10 was not widely adopted, with only around 10,000 units produced. However, its historical significance lies in being the precursor to the AR-15, which was later adopted by the U.S. military as the M16. Recently, the trademark of Armalite was purchased, and a new 7.62mm caliber rifle based on the AR-15 design was reintroduced and sold under the name AR-10 by the new Armalite.

                                                          

Armalite was founded in 1954 as a subsidiary of the Fairchild Engine and Airplane Corporation, primarily focused on developing new materials and designs for the small arms industry. Initially, they quickly introduced many interesting and novel designs. When Eugene Stoner joined Armalite as the chief engineer for competitive shooting weapons and survival rifles, he was also looking for opportunities to develop military rifles.

                                                       

At that time, the Army was testing new rifles to replace the M1 Garand. The T44E4 and heavier T44E5 from the Springfield Armory were essentially modifications of the Garand, while FN provided the T48, which was based on the FN FAL. Although they were late and missed the early tests, Armalite and Stoner decided to join the competition and intensified their development of the AR-10.

Initially, the AR-10 borrowed designs from other rifles. For example, it borrowed the hinged receiver design from the FAL, allowing the rifle to "break open" into two parts for maintenance. It also borrowed the multi-lugged rotating bolt from the U.S. Johnson M1941 rifle and the straight-line stock and elevated sights from the German FG42 and Johnson light machine gun designs. The dust cover over the ejection port was borrowed from the German Stg.44. However, the most significant feature of the AR-10 was its extensive use of lightweight materials such as plastics, titanium, and aluminum, which were commonly used in the aviation industry but not yet in firearms.

From top to bottom: Prototypes 1, 2, and 3 of the AR-10.

The AR-10 was also tested in a 7.62x39mm caliber version, which directly used AK magazines.

                                                       

Most gas-operated rifles move the propellant gas through gas ports in the barrel over a short distance. In Stoner's design, the gas travels approximately 30cm through a gas tube at the top of the barrel into a gas chamber between the rear of the barrel and the receiver. This design, which uses the bolt and receiver as a gas piston, was inspired by the Swedish AG42 rifle. The advantage is the simplification of the gas piston and tube design, reducing moving parts and weight. Therefore, the gas system of the AR-10 consists only of gas ports, gas blocks, gas tubes, and the gas chamber formed by the bolt and receiver. The operating principle of the AR-10 is as follows:

After firing, the bullet passes through the gas port, and some of the propellant gas travels backward through the gas port and gas tube, then enters the gas chamber between the receiver and bolt. At this point, the bolt is still in the locked position, so the high-pressure propellant gas entering the chamber only acts on the receiver, forcing it backward. The receiver has a free travel of about 3mm, and then the chamber pressure drops to a safe level. The unlocking spiral on the receiver causes the bolt to rotate around the bolt axis. As a result, the locking lugs on the bolt disengage from the corresponding grooves in the barrel extension, achieving unlocking. After unlocking, the receiver drives the bolt rearward, completing the extraction and ejection of the spent cartridge case. During the rearward movement, the recoil spring is compressed, and the hammer is pushed down, engaging the sear and locking it in the cocked position. When the receiver travels rearward about 8mm, gas begins to escape from the exhaust ports on the receiver, gradually reducing the pressure. When the gas pressure is completely relieved, the force acting on the operating parts also disappears, but the receiver continues to travel rearward due to its remaining energy until the recoil stroke is complete. Then, under the action of the compressed recoil spring, the bolt moves forward, chambering the next round. When the locking lugs on the bolt reach the corresponding grooves in the barrel extension at the front, the receiver continues to travel forward. Guided by the unlocking spiral on the receiver, the bolt rotates 22.5 degrees to the right, achieving locking. After locking, the rear end of the receiver impacts the sear, releasing the hammer, striking the firing pin, and firing the round, completing the automatic firing cycle.

The AR-10 has 8 locking lugs at the front of the bolt.

Due to the absence of a piston assembly, the AR-10 has fewer moving parts.

Exploded view of the AR-10: 1 - Flash suppressor (also a grenade launcher socket); 2 - Gas adjustment screw; 3 - Front sight; 4 - Gas tube; 5 - Barrel extension; 6 - Charging handle; 7 - Bolt carrier; 8 - Guide rod; 9 - Receiver; 10 - Ratchet ring; 11 - Elevation adjustment screw; 12 - Elevation adjustment screw bolt; 13 - Elevation adjustment screw hole; 14 - Peep sight scale; 15 - Windage correction screw hole; 16 - Recoil spring guide pin; 17 - Buffer tube and recoil spring guide; 18 - Recoil spring; 19 - Handguard; 20 - Barrel; 21 - Bolt; 22 - Connecting pin; 23 - Hammer; 24 - Trigger guard; 25 - Sear; 26 - Trigger; 27 - Selector; 28 - Sear disconnect; 29 - Fire selector; 30 - Sear trip; 31 - Connecting pin; 32 - Grip; 33 - Stock; 34 - Butt plate.

The receiver is machined from aluminum, significantly reducing weight. The bolt locks into the barrel extension rather than the receiver, allowing for a lighter receiver without the need for reinforcement for bolt locking. To further reduce weight, the barrel initially used a titanium inner liner and an aluminum outer jacket, later changed to a stainless steel inner liner and an aluminum outer jacket, weighing only 680 grams. The stock is made of plastic with a reinforced fiberglass shell encapsulating foam. The handguard is made of brown fiberglass, which is lighter than wood. The magazine is forged from corrugated aluminum, weighing 113 grams.

The receiver is also made of aluminum alloy, with a magazine catch on the right side, an empty magazine catch, and selector switches on the left side. The selector has positions for safe (S), semi-automatic (E), and automatic (D) firing modes. The trigger is located between the grip, receiver, and magazine, and the trigger guard can be opened downward to allow for firing even when wearing thick gloves in cold weather.

One of the most notable aspects of the AR-10's design is its layout. In traditional designs at the time, the sight was usually positioned close to the barrel, requiring a downward-sloping stock to align