A good shooting buddy of mine built one that is pretty nice. He used a car axle which he cut and rewelded for a shorter wheelbase. He then welded pieces for the complete carriage. He used well casing for the barrel . He welded a plug in one end and had a piece machined that fits over the breech which gives it a steped appearence and also sleeves the breech for additional strength. This was also welded into place. Then he had the outside machined into the traditional shape of a cannon. It is fairly decent size. It isn't as big as a civil war piece, but you tow it behind a truck on full size car tires. He fires beer cans filled with concrete, or beer cans filled with .50 round balls. I don't remember the charge he uses, but it is some portion of a cup. It is very loud and very dramatic when fired.