A bolt carrier group, or BCG, is a key component of an AR-15 rifle. Its primary purpose is to act as a housing for the bolt and carrier assembly, which are the parts of the rifle that chamber and fire rounds. The BCG also helps to ensure proper cycling of the action and houses the firing pin, extractor, and other critical parts. In short, without a properly functioning BCG, your AR-15 rifle will not work correctly.
The bolt carrier group consists of three main parts:
The carrier itself is generally made from forged steel or aluminum and contains channels that help guide the bolt and gas key into position. The actual bolt is usually made from high-strength steel and is what locks into the receiver to ensure a proper seal when chambering a round.
The final part of the BCG is the gas key, which is attached to the carrier and helps to channel gases from the fired round into the action to cycle it.
It is important to note that bolt carrier groups come in two different types: full-auto and semi-auto. Full-auto BCGs are only for use in firearms that are capable of fully automatic fire, such as machine guns. Semi-auto BCGs can be used in both semi-automatic and fully automatic firearms.
