In the Marine Corps, the M240G is the predecessor of the M240B. The main differences between the two machine-gun variations is the Picatinny rail system, hydraulic buffer inside of the butt stock to reduce the amount of recoil felt by the gunner, and the number of gas settings on the gas regulator plug. The M240G has three gas settings, allowing the machine gun to have a fire rate between 650–950 rounds per minute depending on the setting selected, whereas the M240B only has one setting, restricting the fire rate to between 550–650 rounds per minute. The smaller gas port used on the M240B slows down the rate of fire, which increases the longevity of the machine gun by reducing stresses on the action. A side effect is a weapon that will not fire when extremely dirty as the energy on the piston is reduced. The Marine Corps relies on fire discipline among its machine gunners to not set it to the largest port unless required.