May I recap this thread, and ask if the cannon traversed okay before making adjustments to the switches?. If so, and it's become erratic since, then maybe reverse the adjustment. The round plate which operates the two switches is designed to show the gun at Home (both switches closed), and Mark (both switches Open) with the motor stopping when it sees the Home situation.
I've finally thought to look at the drawing of the cannon assembly; the upper portion, the trough or 'magazine' and the kicker solenoid, seems to be fitted onto the motor shaft with slots fitting over a pin on the shaft, without facility for adjustment. However, the cam/switching components seem to be attached to the motor with a collar. This is drawn with what looks like a grub screw showing in it. I think that this may allow the entire cam plate to be adjusted relative to the motor shaft, and the trough up above. Thus allowing the switches to be adjusted (or re-adjusted) for reliable calibration, and then the trough to be aligned with the feeding track by moving the cam plate, so that the motor moves over a little more (or less, depending on the direction of adjustment) before the pin on the cam closes the Gun Home switch. Similar, in a way, to moving an old-fashioned car ignition distributor while it's meshed with its drive shaft, to tweak the spark timing.