That's a great risk vs reward concept. I'm afraid that it being able to get primary ammo as a heavy is a bit overpowered. What I propose is to put it on the level of an auto rifle but kills give bonus damage and add crowd control as well. 10 consecutive kills will put on par with other lmg's but it would still have room to stack 3 more times. In pve, this weapon would be amazing and the only reason someone would use this for pvp is to be able to be able to carry an auto rifle along with other primaries.