The bolt holds the round in place ready for you to pull the trigger, which releases the hammer. The hammer strikes the back of the firing pin pushing it through the bolt to strike the primer on the round thereby firing it. The bolt is subjected to the highest amount of stress in your AR.

For that reason, don’t go cheap when choosing your bolt. Rather than go with Carpenter 158 steel for your bolt, FSD recommends 9310 steel. The Carpenter steel is just too brittle. Sure, the 158 is cheaper, but it WILL break – and when it does, your gun is down until you find a new one.

A firing pin is a movable pin in a firearm that strikes the primer of a cartridge to set off the charge. In the case of the AR-15, it is located in the bolt carrier group and can be easily exchanged in the event that it is damaged or ceases to function properly.

In the AR-15 bolt carrier group pictured here, the firing pin is the silver-colored item in the middle of the picture.

In the AR-15 bolt carrier group pictured here, the firing pin is the silver-colored item in the middle of the picture.