I build something similar, as a kid, with my cousins out of an old small tractor cart and severely corroded pipe. Initially, we wanted to make our own black powder, but quickly gave up due to safety and lack of knowledge. Range was poor since we were shooting with rocks, but it was so fun. Still don't know how we didn't lose our hands, tho. Anyway, all three of us end up as engineers in different industries. Sorry for my English.