Which part of the M249 AR pulls moving parts rearward and is fixed to the right side of the receiver?

The cocking handle assembly of the M249 Automatic Rifle is crucial for the weapon's operation, as it is responsible for pulling the moving parts rearward, which is essential for chambering a round and preparing the weapon to fire. This assembly is fixed to the right side of the receiver, providing the operator a straightforward mechanism to cycle the action, chamber a round, and reset the weapon after firing. Its position and function are designed to support efficient weapon handling and reliability, which are critical during combat operations.

The firing pin assembly, while important for firing the weapon, does not play a role in the movement of the bolt or charging of the weapon. The loading handle, commonly associated with the M249, is not a standard term used for this function and may lead to confusion; it primarily refers to the mechanism for chambering the first round but does not pull the moving parts back in the same way. The feed tray assembly is involved in the ammunition feeding process but does not contribute to the rearward movement of the bolt assembly. Thus, the cocking handle assembly is the correct component for this function in the M249.