AR-15 Bolt Carrier Group
The Bolt Carrier Group is a master of multitasking, it is what makes an AR-15 rifle semi-automatic. Relying on the gas created by the explosion of a spent round. The Bolt Carrier Group ejects the spent shell, strips a new round from the magazine, feeds the new round into the chamber, locks the bolt back and cocks the hammer. So how exactly does this work?
Thanks to Eugene Stoner’s clever design, it is actually fairly straight forward! Let’s break the cycle down into stages to see exactly how it works, assuming that the operator has already manually chambered a round with the charging handle:
- The trigger is pulled, the hammer strikes the firing pin and the bullet is fired.
As the bullet travels down the barrel it carries with it the gaseous byproducts of the explosion that fired it. This gas is forced into the gas port, down the gas tube and back into the bolt carrier key.
- The gas enters the Bolt Carrier from the Bolt Carrier Key and forces it backwards. As the bolt carrier moves backwards, the gas pushes the bolt itself forwards, rotating it slightly and unlocking it from the chamber lugs in the process.
- The spent case is pushed from the chamber through to the ejection port, where it will pivot on the extractor hook until it is ejected from the weapon.
- While the spent casing is being ejected, the bolt carrier is still moving backward into the buffer tube. At this stage the hammer is once again cocked.
- At this stage the pressure of the buffer spring begins to push the bolt carrier forward once again.
- During the forward motion of the bolt carrier, it strips another round from the magazine and feeds it into the chamber.
- The new round locks into the chamber as the extractor clamps over the rim of its casing.