Blow Up The World

Pictures were taken, and can be viewed here.
The heavy-looking rifle being fired from the tall stand is a 2-ga. 1.312" dia, 1/2 lb of lead per shot.
Regarding my mortar:






Here it is, and it works really well. Here's some info:
1. I built it from a solid billet. Wall thickness is approx equal to bore diameter. Overall diameter is 7".
2. Barrel length is 14 inches. It's as big as I could get on my little lathe.
3. There is a powder pocket in the bottom of the bore. This makes ignition more reliable. It's about 1" deep x 1" dia.
4. Here's a print of a barrel someone else is making. Note the 1" barrel wall thickness.
5. I use a film can (35mm still camera! about 500 gr.) full of ffg powder, with a pop can full of cement. This weighs about 1.5 lb. Works well in a short barrel.
6. This gun, coincidentally, also fits a tennis ball nicely, with no wadding. A tennis ball filled with lead weighs about 6 lb. The recoil from this will break a 1" oak axle.
I build a cannon once from the injection tube from an injection molding machine. It was 4130 or something like it, and hardened. 6' long with a wall of 1.5 inch, as I remember. Worked well, but remember that this was NOT pipe in any sense of the word. More like hydraulic cylinder.
Using modern steels, you want to try to keep the wall thickness to at least half the bore diameter, and keep the loadings modest. These things are for fun, not actual warfare.
Mine uses #11 percussion caps. Yes, they will reach that far.