a throttling valve develops a pressure to bring recoiling parts of a weapon to rest with a constant force . counter - recoil is provided from recuperator pressure . the throttling valve is biased with a force proportional to the sine of the gun elevational angle to compensate for the gravitational component inline with recoil . counter recoil force is controlled by a valve that regulates the recuperator pressure available for counter - recoil by an amount that is proportional to the sine of the gun elevation angle .