This article covers a subject that has been deemed non-canon by either the author or the Alien vs. Predator licensees, and thus should not be taken as a part of the "real" Alien vs. Predator universe.
"Alternate ammo type, typically used by USCM snipers; propellent-assisted rounds exit the rifle's barrel at a significantly higher velocity, causing tremendous damage."
The A19 is a ammunition type which send propellant-assisted rounds that exit the end of rifle's barrel at a significantly higher velocity than the standard ammunition which causing tremendous damage. However it gives the weapon a stronger recoil, thus reducing its rate of fire.