>I'm doing kind of a similar thing with .308/7.62x51mm ammo in WARS, changing 5mm to be a lower power "surplus" 7.62x51mm round. It does a hell of a lot more damage than vanilla 5mm, but still less than .308. So if you come across a minigun with dozens or hundreds of surplus rounds in tow, you can use those in battle/sniper rifles, but they'll do a lot less damage (and probably be less accurate and gunk the weapon up faster). Then, it goes without saying that you also add some 7.62x51mm that is more powerful than the regular type, that happens to make more damage and gunk up the gun slower. More expensive -sure and rarer too. Seems only balanced to me.