Lots of Trooper fire.
The Assault rifle is a beam that is used by most types of Pirate Troopers in Metroid Prime 3: Corruption. It is a small beam that is the basic armament of each type of Trooper. It serves as an upgrade to the Galvanic Accelerator Cannon. The beam contains a fuchsia core, surrounded by blue and green energy.
The Assault Rifle can fire approximately 3 beams per second. However, most Pirate Troopers tend to only fire quick bursts of four or five rounds before they maneuver their position.
The beam's purple color suggests that it is similar to the technology of the Wave Beam, or perhaps a Pirate-adapted form of the Plasma Beam. It deals little damage to Samus, but the lack of power is compensated by the speed and sheer number of the Pirates attacking her.
The Galactic Federation 07th Platoon uses their own assault rifle, but it is very different from that of the Pirates.