The Sawed-off over/under shotgun
is Winchester 12 Gauge Double Barreled Shotgun, whose barrel was shortened.
In Inglourious BasterdsEdit
When "The Basterds" break Hugo Stiglitz out of jail, Donny Donowitz carries a sawed-off over/under shotgun, using it to shoot a German soldier guarding Stiglitz.
Eli Roth poster with the shotgun.