By Eric Adams; Photograph by John B. Carnett
WHAT HAPPENS WHEN YOU FIRE?
1. The shooter pulls the two-stage trigger, which releases a heavy, spring-loaded hammer. (The first stage is a resistance point, the second is firing. Less motion to actually fire helps the shooter precisely gauge when the shot will go off.)
2. The hammer strikes a firing pin, which rams the back of the bullet in the chamber—in this case, a 5.56 NATO or .223-caliber cartridge, both common, inexpensive rounds for hunting, military, and police purposes.
3. The impact ignites a chemical mixture—called a primer compound—inside the cartridge, causing the gunpowder to burn rapidly and increasing pressure inside the cartridge until it forces the bullet down the barrel.
4. High-pressure gas from the burned gunpowder vents through a hole in the top of the barrel, through the gas valve and into the gas tube.
5. The gas pushes the operating rod rearward, which in turn knocks the bolt carrier backward. This rotates and unlocks the bolt from the barrel so the spent cartridge can be ejected and replaced with a fresh round.
6. The bolt carrrier’s movement triggers an extractor to grab the rim of the spent cartridge and pull it against an ejector (a small bump inside the receiver), which hurls the case out of the bolt. The same rearward motion also recocks the hammer.
7. A recoil spring in the gas tube brings the operating rod back to its resting position, pulling the bolt back. The bolt pulls another bullet from the magazine and slides it into place for the next shot. A cam rotates the bolt to lock and seal the cartridge in the chamber.
8. If the rifle has a fully automatic mode—civilian competition-shooting versions do not—a single squeeze of the trigger allows this process to repeat uninterrupted, at up to 900 rounds per minute, until the bullets are gone.
