The Model 12 is a pump action twelve-gauge shotgun, iconic in that it has the classic features that make a pump-gun so appealing. And it may not be the first, but it certainly trained generations how to shoot airborne game among many other things. The Model 12 was also used by the US Military, making it an actual war weapon unlike your AR 15.  The model 12 uses traditional wooden furniture, with an easily identifying ribbed front grip. A shallow rib runs the length of the barrel, with a targeting bead on the muzzle end. The barrel itself is a thirty-inches long and has a three-inch magnum chamber. It features a familiar safety at the front of the trigger guard, and an action release just behind it. The tubular magazine holds six 2-3/4 shot-shells, and it is clamped to the barrel at the front of the tube.
I looked up the serial number and if the internet is to be believed, this gun was manufactured in 1917, making it a hundred and five years old.