Assault Rifle
From WikiRaider
An Assault Rifle is an automatic weapon that fires rifle-caliber rounds. The Assault Rifle can trace it's origins to World War 2, where they were first used by the German Army. Today, Assault Rifles are the standard small arms of most modern armies.
We see assault rifles a few times in Tomb Raider, the first time in Tomb Raider II with the M16.
Underworld
The RC650 Assault Rifle can be used throughout Tomb Raider Underworld.