to be opened for cleaning much like a break-action shotgun. The ejection port cover is similar to that found on the German World War II-era StG44. The bolt locking mechanism is similar to the M1941 Johnson rifle (itself an adaptation of the Browning-designed Remington Model 8 bolt). From the German MG 13 light machine gun, FG 42 and M1941 Johnson machine gun came the idea of the straight-line stock layout. A "straight-line" recoil configuration increases controllability during burst or automatic fire by reducing muzzle climb. The AR-10's method of rotary bolt locking, straight-line recoil, and gas operation enhanced its inherent accuracy. The original AR-10 action (later developed into the ArmaLite AR-15 and M16 rifle) designed by Eugene Stoner is commonly called a direct impingement system, but it does not utilize a conventional direct impingement system. In , the designer states: ″This invention is a true expanding gas system instead of the conventional impinging gas system.″ The gas system, bolt carrier, and bolt-locking design were novel for the time. Most gas-operated rifles divert combustion gases from a port in the barrel to a piston and cylinder arrangement adjacent to the port. In Stoner's design, the gas travels from a port near the middle of the barrel through a steel tube back into the receiver. The gas enters a chamber inside the bolt carrier formed between the rear of the bolt and the inside of the bolt carrier. The bolt within the bolt carrier is fitted with piston rings to contain the gas. Once the bolt carrier moves to the rear a small distance, excess gas is vented through holes in its side. This use of the bolt and bolt carrier for the separate actions of a piston and gas cylinder simplified construction and saved weight. Movement of the bolt carrier was in-line with the bore, greatly improving inherent accuracy, as well as keeping the rifle on target as the gun fired. Since the straight-line stock placed the shooter's eye well above the barrel the rifle's sights were mounted high, with the rear sight and elevation wheel calibrated for 7×51mm NATO for specific range settings contained in a carrying handle that also protected the cocking/charging lever. Windage was zeroed by drifting the rear sight. The receiver is made from forged and machined aluminum to reduce weight. The bolt locks into an extension on the barrel instead of the receiver allowing for a