HOME RULES FROM THE REDDIT TREAD
Damage rules and range are same as an Empire GC, but he misfires on a roll of 1-3. Then roll a D6:
1: SPLAT: The cannon and bearer explode in a shower of gore and metal. Any models within 3" suffer a S5 hit and the bearer is slain.
2: CRACK: The cannon splits in half and the cannonball hits its bearer on the head. Cannon out of action, bearer counts as stunned hereafter, roll a leadership test to revive after 1 turn.
3: The cannon fires but flings its bearer backwards D6". Any models in a semi circular arc behind it within that distance + the bearer suffer a S4 hit.
4: The cannon misfires and, enraged, the bearer charges D6" towards the nearest visible enemy model.
5: KABOOM as on 6 of normal table.
6: FIRE ME AGAIN!: As kaboom but, in a masochistic frenzy, the bearer insists he then be fired again. Roll to hit as usual, re-roll further 6's if misfires again.