[Dtq]

It could be:

1. Battery problem, change the battery.
2. Bad motor, you need to change it, it'll stop working eventually.
3. Motor adjustment height. If the motor is too high, lower it, it needs more power to work if it's too far up there.
4. Wiring, faulty wiring, could make your gun consume more power. It needs to be changed.

Take your pick. It could be any number of these. I can't think of anything else. For now...