Something I cooked up one night when I was terrifically bored.
SPSM stands for Special Purpose Shotgun, Modular.
Anyway, pretty straightforward gun - fires lots of meat-shredding pellets in a octagonal pattern spread.
The unique thing about the '11 is that, as its name suggests, it's modular - you can swap out the upper and lower receivers, just like a rifle. The standard lower uses a tubular magazine, but the entire weapon can be modified to use a six-round translucent plastic box magazine by swapping out the lower receiver.
The weapon features a flattop Picatinny rail system - no built-in ironsights. Backup diopter ironsights are mounted by default. That box on the top is a red dot sight.