I made it out of an inert .50 caliber sniper round that I bought online.
I made the bowl out of the projectile itself and the rest is the casing, the choke is located where the firing pin strikes the round to ignite the primer. I drilled a hole into the side of the casing and used a C-clamp to wedge the bullet in place.
I'm still trying to think of a name for it, so far all I've come up with is the obvious "The Sniper". If you have any ideas let me know.