The Modular Reciever A, v1.3, is the more common Reciever in Set 1 and has many different components for it. Some are proprietary and can only be used with this MR. It utilises a short-stroke, gas-powered piston that is connected to a rod extending backwards to a keyhole in the recivers front face. Short-stoke operation means that the distance the piston travels is less than the diameter of the cartidge it fires. When fired, the gases from the round's primer ignition travel along the barrel until they enter a small trap in the top of the barrel. There, they are forced against the piston head, pushing it backwards as the gases expel themselves in small holes along the piston's body, never going further into the operation than that. The inertia of the gas, however, pushes it(the piston) back