When I fire paintballs out of my
XM001 the spread at 25 yards is somewhere between one and five feet with a flat trajectory. I’ve never fired tried it for range but on my first cannon which hade a three foot, 150cal barrel at about 50 the spread was about five yards, give or take a few yards it’s been awhile, with a high trajectory.
But from what I’ve heard the average grouping of medium to heavy artillery at maximum seems to be about 20-30 yards at about 80 yards, that’s what I read in a review on a cannon I found somewhere on the web, can’t remember much about it, it’s bean awhile.
My opinion is that using cannon as a scattergun doesn’t work to well because not all the paintballs break, scatterguns work best at short ranges. Use grenades, I make HE grenades out of a short section of those balloons that clowns make animals out of (those long ones) there somewhat accurate (especially considering the fact that elongated projectiles and smoothbores don’t mix), have nearly twice the range, and have a surprisingly large blast radius. Or you could buy frag grenades (tipman squad busters, pod rockets, etc.) and use a larger bore, that would probably be your best bet, as ammo would be somewhat easy to acquire and would have good range and a large blast radius.
Do some research on cannon ammo used during the American civil war, the Napoleonic wars, ect.