RandyRay41,
That pic above was a Titleist #3, IIRC, shot with 480 grains of Pyrodex RS, some corrugated cardboard discs cut to size with a compass and scissors, for use as wadding, and a torn t-shirt patch wrapped around the golf ball. We were using some cannon fuse so that no one's hand would be around the touch-hole, but you could also use some priming powder and slow-match.
On a couple occasions we've also used 4-5" sections of PVC filled with concrete, for a wadcutter effect. The pressure gets pretty high with heavy projectiles. I prefer the golf ball for ease of procurement...if you tell your buddies you're breaking out the cannon, they WILL bring you golfballs....call it the price of admission.
My particular cannon does not have an undersized chamber drilled behind where the ball is seated. This means that in order to get an even powder-burn in the chamber, you need to have 1.75"diameter x 3.14"for area x____amount of height of propellant...making a cylindrically shaped charge to propel your projectile in a consistent manor so that you can achieve a degree of consistency and accuracy...or at least as much as possible with a smooth bore.
480gr gets you a big boom....i like to hear echo....then silence.....then cautious laughter...then uproarious laughter. (works every time!)
That powder load, as you can tell from a look at the picture, doesn't get entirely burned up in the barrel, where the magic happens as far as the golf ball is concerned...but a few, say 8-12, extra feet of muzzle flash and ensuing smoke cloud is always a crowd pleaser.