Bolt Carrier

Bolt Carrier / Bolt Carrier Group (often referred to as BCG) is a key moving component of a firearm responsible for cycling the weapon during firing. In AR15 rifles (real firearms), the BCG handles feeding, locking, firing, unlocking, and ejecting the cartridge (or feeding BBs and generating recoil in airsoft gas systems). The Bolt Carrier Group is therefore the heart of semi-automatic and automatic weapons built on the AR platform. It controls the complete firing cycle and significantly affects reliability, handling, and shooting feel. In airsoft, the BCG is a crucial element of realism and one of the most important components of GBBR rifles, as it carries the nozzle and transfers recoil energy into the stock.

Real steel bolt carrier group for an AR15 rifle

What the Bolt Carrier Group (BCG) consists of

The BCG is not a single part, but a complete assembly of several components:

Bolt Carrier: the main body that houses the other parts and moves inside the receiver.
Bolt: locks into the barrel extension, carries the firing pin, and performs the actual locking / unlocking.
Cam Pin: converts the linear movement of the carrier into rotational movement of the bolt.
Firing Pin: strikes the primer (in airsoft replaced by the function of opening the gas valve).
Retention Pin: keeps the firing pin securely in place.

How the BCG works during firing

After the trigger is pulled, the following cycle occurs:

the shot is fired (or, in GBBR systems, the gas valve opens),
gas pressure drives the bolt carrier rearward,
the cam pin rotates the bolt, causing unlocking,
the cartridge case / BB is ejected,
rearward movement compresses the return spring,
on the forward stroke, a new round is chambered and the bolt locks again.

This cycle happens in a fraction of a second and is essential for the smooth operation of semi-automatic and automatic weapons.

Operating principle of an AR15 rifle

BCG in real firearms vs. airsoft

Real firearms: The BCG operates under high pressures, is made from hardened steel, and is one of the most stressed components of the weapon.

Airsoft (GBBR): The BCG simulates real operation using gas. Materials vary:

Aluminum: lower weight, faster cycling (higher rate of fire).
Steel: higher weight, stronger blowback, more realistic operation.

In AEG rifles, a true BCG does not exist – its function is replaced by the gearbox with a piston and gears.

Upgraded bolt carrier for Marui MWS / CYMA CGS rifles by Guns Modify

The importance of the BCG for weapon function and behavior

Reliability: build quality affects feeding, malfunctions, and service life.
Blowback: BCG weight directly determines recoil strength in GBBR rifles.
Cycle speed: lighter carriers = faster return, heavier = more stable operation.
Wear: a poorly made BCG can damage the receiver or trigger components.

BCG as an upgrade part

In airsoft, the bolt carrier is one of the most common upgrade parts, especially for MWS / CGS-type systems. Replacing the BCG allows you to directly influence:

realism of operation,
rate of fire and trigger response,
longevity of internal components.