Like tropico , I want one! (even if it does not work out to be hand fireable)
Remember that the recoil is a product of the weight of the projectile, the weight of the "cannon" and the velocity of the projectile- so the lighter the ball the less the recoil.
what did you bore it to?
maybe one of those little (6mm) paint balls would work, they are very light(2.5 grains)
And a roman candle ball is 4.0 grains
Have FUN! & LET us know what happens!
Merry Christmas!
Santa Dave