[BHOP]

I would recommend taking the load off the motor using a mechanical device like others have said.

I'm not sure which locking pins they are talking about in the window motor, but I do know they utilize a worm "drive".

You can read more about them on wikipedia (search worm drive), but if the window motor won't give you enough power to move the device using to hold your shooter(not hold it in place) then buy your own worm and worm gear(mcmaster,etc) and make your own worm drive with a more powerful motor.

"Worm gear configurations in which the gear can not drive the worm are said to be self-locking. Whether a worm and gear will be self-locking depends on the lead angle, the pressure angle, and the coefficient of friction; however, it is approximately correct to say that a worm and gear will be self-locking if the tangent of the lead angle is less than the coefficient of friction."

This is pretty much a super high gear ratio, but typically you will see self locking effects from a worm drive device meaning you DON'T have to provide a constant torque to hold your device in place.