I got a call one day from a customer who brought me a Master #40 padlock with a rotating shackle that for some reason, could not be opened with the original key. It seem like the key only starts to turn the shackle but soon would bind up. As it turned out, the cam on the rear of the plug had come loose and jammed the mechanism. Since the lock was attached to a specialized hasp, the customer requested it will be removed.
In order to solve this issue, the lock's plug would have to be drilled out. Once I did that, I pushed the remainder of the cylinder to the left of the opening in the lock case. While I was looking through the hole that I drilled, I could see the notched end of the locking dog. Using a small screwdriver, I pushed down on the notch which released the shackle. Next step I used a small screwdriver with a 90-degree bend in it in order to rotate the shackle clockwise until it got unlocked. The opening process went quickly and smoothly. The only thing I had to pay attention to was that the locking dog, which is spring loaded, will not reengage before the shackle could be rotated to the open position.