Okay, I have to say, that cannon is as cool as can be. How much powder does it use? Naturally I'm assuming you don't fire solid shot out of but what would it shoot?
So far, we have only used that one for "blank" firing in demonstrations such as seen in the first photo, for which we normally use a 3 ounce charge ... It is a 2 1/4 inch bore, cast iron but the tube is cast around a high-pressure steel liner (smoothbore) so it presumably could be used to fire projectiles - we just haven't tried that (yet).
Our other gun is a 1/2 scale version of the British 9-pounder RML gun, made about 30 years ago by an engineer - its barrel is also smoothbore (2") but all steel, and the gun is roughly the overall size of an original 6-pounder. We do use that one to fire projectiles on occasion, using 2" steel round stock cut off in 2" lengths - not the most aerodynamic projectile, but it will punch right through a vehicle body at 150 yards or so! This is the smaller gun -