Here's another one I built. I bought the barrel, and built everything else from scratch. I have a coal forge, and used that for a lot of the parts. The barrel is 24" long, weighs 40#. The carriage weighs another 38#. It fires a 1" diameter, roughly 1/4# ball. Not terribly accurate, but I can usually hit a garbage can at 200 yards. It'll put a hole on a tree you can put your fist in at that range. Recoil will drive it back over three feet on mowed grass.
I haven't tried hunting with it yet. I've also found 10 .50 cal balls makes an interesting load.
They don't let me use it at the range, so I'm limited to the back yard (I live in the country). The first time I shot it in the yard, I literally rattled dishes in my neighbors cabinets 1/4 mile away, and they thought my propane tank had exploded...
I do mention home protection at times as a way to justify purchases... I have the biggest gun on the block, hehe!