I'm not a gearbox expert but as far as I am aware, a motor draws almost infinite current at 0rpm. so if your motor is seized or something is stopping it from spinning AND there is power running through it, it's most likely drawing from the power source at an insane rate. which might explain the extreme heat up. As to what is seizing the motor... that I am not sure. maybe try adjusting the screw at the bottom of your pistol grip. The height of the motor might be off.
also, did you clear the barrel with the cleaning rod? its possible that there is a jam
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