The Karseus was selected as the standard assault rifle for the NHDF troops after 5 years of extensive trial and development by the NHDF.
Based on the turian Phaeston, the original design was adapted for use by multiple species and improvements to the lackluster damage of the original were made at the hands of the developer and supplier Valerion Kinetics without sacrificing heat capacity. With more damage came more recoil but this wasn't viewed as flaw considering the Phaeston's almost nonexistent recoil.
The Karseus can be fired at full automatic, but it is set and usually used in its three-round burst mode. While most common within the Red Rift cluster, this weapon can be found at the hands of various terminus factions since Verlerion Kinetics has sold this rifle to private companies as well as to the NHDF.
Common variants include under-barrel grenade launchers and concussive mods intended for crowd riot control.