Bio-mass, a radioactive orange-red substance, serves as the ammunition for most of the Drudge weapons, such as the Strike Rifle, Striker, Shrieker, and Warp Pistol. Smaller bio-masses are used as Radiation grenades. Not much else is known about it, except for what Prometheus told Michael Ford: "Drudge weapons utilize a unique bio-mass that can be converted into a variety of damage effects. It's far more versatile than a plasma core and several times as deadly."
Bio-mass can be seen in the center of the Strike Rifle.