humped gun for sure..like the USMC mark on the stock...iv held many genuine Mark1s and have yet to see that stamp...make ist real rare.
an observation on the finish.
the genuine guns iv seen
the action slide arm were blued, bolts blued, notice the trigger has rust. and the rest of the gun is perfect? so..just the trigger and safety rusted...not the rest of the shotgun.
butt stock should have a wide swivle like the M40 and 513T..
Barrel should be Ord marked, and serialed to the action...
buy a bayonet lug, park it, stamp it..get rich at it...yea.