Bolt Carrier Group
The Bolt Carrier Group is a component of an AR platform rifle. The BCG consists primarily of the Bolt Carrier, the Bolt and the Firing Pin.
When loading, the BCG is propelled forward by the buffer and buffer spring, stripping a cartridge from the magazine, pushing the cartridge into the firing chamber, and then rotating the bolt to lock the firing chamber closed.
When the trigger is pulled, the hammer strikes the back of the firing pin in the BCG, causing the firing pin to impact the cartridge primer, firing the round.
After firing, pressure from the expanding gasses of the now burning cartridge propellant is directed into the “key” of the bolt carrier, pushing the carrier to the rear.
As the bolt carrier travels to the rear, it rotates the bolt to unlock it from the firing chamber, then pulls the bolt to the rear which extracts the spent cartridge case and ejects it through the ejection port.
The top of the bolt carrier also pushes the hammer to the rear, cocking the rifle and preparing it for the next shot.
After the bolt carrier reaches it’s rearmost travel, it is again pushed forward to strip and load the next cartridge in the magazine and prepares for the next pull of the trigger.