Always get heavy ammo. When it appears, don't pick it up just stand close enough to where it appears as a purple brick on the floor. After that, wait a minute and watch the kill feed. When u see a few enemies have died after the heavy ammo drops then pick up your heavy ammo. You will be one of maybe 3-4 guys left with heavy. Then just play smart and pick your engagements. Don't rush and pick an area with cover and hopefully u can get at least a few kills with your heavy then.