[BenG]

Don't use valken products?

all jokes aside, you might have a loose connection that is expanding when it heats, as it heats its pulling apart and making less and less contact. Have fun with this witch hunt. Check the fuse to start with, although its highly unlikely as fuses are designed not to make any contact at all when they blow, (or they wouldnt do their job) but you might have a miracle.

This is just one possibility, you could have dead spots in your motor, although ussually when a motor dies it spins until it lands on a dead spot then doesnt move again, but you may have the same problem wires expanding when heated. you could also have such a high amp draw that your draining the battery below its threshold and your buddies gun has a low enough amp draw that the battery works, but highly unlikely has you have tried other batteries and stock guns should not be drawing that much power, that said check your motor height, if its off you might be overdrawing, does the battery get hot when you do your 5-10 weak shots?