To fire the weapon, the trigger must be held down for a couple of seconds.
The XM99A Phased Plasma Pulse Rifle is based on boasts made by Hudson in the extended Special Edition of Aliens. The dialogue in question ("phased plasma pulse rifles") is itself a reference to the gun shop scene in James Cameron's earlier film The Terminator, where the Terminator (Arnold Schwarzenegger) asks for a "phased plasma rifle in the 40-watt range".
"ARMAT XM99A" can be seen on the weapon's stock when sprinting with it.
In-game, the XM99A has to be charged up before it will fire; players must hold down the trigger while this is happening, otherwise the weapon will not fire.
As with all DLC weapons, the XM99A cannot be customized and "ATTENTION This weapon cannot be customized" will be displayed when an attempt is made to do so in the Marine Loadouts menu. However, the weapon is equipped with a 2x Telescopic Zoom Sight by default which cannot be removed.
Although the XM99A is always equipped with a 2x Telescopic Zoom Sight in-game, the photo of the XM99A in the Aliens: Colonial Marines Brady Games guide lacks the scope.
Despite it's slight delay between trigger pull and firing, the rifle is extremely powerful. All basic enemy types such as Warrior xenomorphs and PMC's can be killed with a single shot anywhere on the body. Stronger enemies such as Lurkers and Smartgun PMC's require two or more shots.