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When using the AR-15 family of rifles, all three of these alternative calibers use the same bolt carrier group (BCG) and upper receiver as the standard 5.56 x 45 rifle. The 300 BLK requires the forward-most alignment ribs inside the NATO STANAG magazines to be removed, due to the larger diameter of the bullet.
The resulting COAL of 2.300" is only 1.02 mm longer than the maximum COAL for chambering a cartridge in the smaller AR-15; however, the 45 Raptor chamber pressure is allowed to be as high as 62,000 PSI. This means that the stronger AR-10 receiver and bolt carrier group is needed for shooting this cartridge.
The operating rod is connected to the bolt carrier group and rides through a machined boss in the receiver rail system interface, keeping the bolt carrier in a linear plane as it operates. This eliminates carrier tilt. A spring-loaded dust shield mounted on the bolt carrier allows the bolt carrier to return to ready position.
The rifle features a short-stroke piston mechanism as opposed to the semi-direct impingement system of the AR-15. Gas flow is controlled by a four position regulator. Several key parts, such as the gas piston, gas regulator, and bolt/carrier group are chrome plated. The bolt carrier features an integral lug in place of the AR-15's gas key.
The Armalite AR-15 is the parent of a variety of Colt AR-15 and M16 rifle variants. History After World War II, the United States military started looking for a single automatic rifle to replace the M1 Garand , M1/M2 Carbines , M1918 Browning Automatic Rifle , M3 "Grease Gun" and Thompson submachine gun .
The receiver is made of forged 7075-T6 aluminum, while the 14.5 in (368 mm) barrel, bolt, bolt carrier, and fire control group are made of steel; these components can be easily serviced and replaced by unit armories, enabling the addition of enhanced components and thus making the platform readily upgradable.
The "bolt head locking lever" is a spring-loaded claw mounted on the bolt carrier that grabs the bolt head as the bolt carrier group goes into battery. The lever essentially ratchets into place with friction, providing enough resistance to being re-opened that the bolt carrier does not rebound.
However, the bolt handle can be manually worked to hold the bolt back. FNC magazines will function in AR-15/M16-type rifles but the follower will not hold the bolt open on the last round unless they have been modified with an M16-type follower. [5] The plastic-coated, lightweight alloy skeleton stock folds to the right side of the receiver.