Quoted from Excalabur:I'm afraid I don't have access to an AC/DC at the moment--I recently moved continents. But there's a set screw in there somewhere that adjusts the cannon height. It's a bit of a bitch to get to, if I recall correctly, though looking at photos the screw head might be accessed from the top. Look just behind the post.
Stern tech support should be able to tell you where that is if you can't figure it out. Sorry!
The set screw keeps the cannon in place - you cannot adjust the height of the cannon with it. The only way to adjust the height is to add washers to the shaft to raise the cannon up.