Like all +1 weapons, the DM adds +1 to the AC hit when using this weapon but the damage bonus has already been factored into the damage wheel.
If the attack would have hit the intended target and the 💣 is closest to the damage dot on the combat board, this weapon misfires and deals 2 points of damage to the wielder. Misfires deal zero damage to the intended target. Misfire damage is not altered by ability scores,