The Virginian, is correct. The first motion of a fired pump gun, recoil sends the gun back, the forearm is in your hand or resting on something, this causing the forearm to be pushed forward, which unlocks the bolt. Now with about 7 lbs of gun moving toward your shoulder with say 30 foot pounds of energy, you stop that motion, except for the bolt which was unlocked when the forearm was pushed forward or more accurately left behind, the bolt continues aft ejecting the shell. Virginian in LA is exactly correct. If the OP or his father in law would shoot the gun moving objects they would not have noticed the inertia since the gun would not be arrested as quickly.
Single Six, The standard gunsmith test for pump guns involves, in a safe direction, pull the trigger on an EMPTY gun while holding the forearm firmly back. If all is well the forearm will not come back until you nudge it forward then pull back. If the mossberg passes this test there is nothing wrong with it.
Last edited by birdshot; November 14, 2012 at 03:41 PM.