Just tried to do the Deputy Crackshot skill challenge and even if you hold the power until the bar is full you can see the cannonball explode almost immediately, on the further back cannons it explodes half way between the cannon barrel exit and the wall on full power.
On top of this which ever cannon you choose to use half the time you end up controlling a different cannon from the one your at and after a while of shooting it completely stops working, when you hold and release 2 the cannon doesn’t fire and the cooldown still activates