Note on setting the over-toggle ("over-toggle" is the official Crosman engineering term for this) of the pump arm. First; it isn't essential but I always check this with the internals out of the gun so that there is no back pressure. You want the pump head to hit the back of the compression chamber then add about 1/8th more rotation. Normally, I do this by feel; it can be clearly felt when the over toggle occurs and you want to set it just a tiny bit past that point. No other adjustment is needed. Like I said, don't worry about the air hole unless there is an obvious problem in operation. If that air hole ain't working right, there will be no missing it in operation.


Checking the check valve: One test of the check valve operation is to pump the gun up to full pressure and then pull back the pump arm and just let it rest there on the bubble of air and observe where it is. If the check valve is slowly leaking, the pump arm will move up.

Trying out the pump arm from the well performing 108 in the 107 might be helpful to determine if the rebuilt pump head is working at high pressure. When I had a low performing gun and everything else was okay, I always suspect that the pump head was leaking at high pressure. Thinking about your rebuild, if the brass ring is not pushed back completely and solid, air will leak past that point.