thats only going to put 7.4V on the bulb, wich normally likes 12V, i think the best idea would be to put 3 300s batterys in the m4 using a one cell extender from lighthound. this should fit just fine if not some small magnets could be put between the cells to fill the small gap. i have wanted to do this mod forever but i cant justify a m4 when i can make a ROP LE for less than $100