AUG HBAR

The Steyr AUG or, its variant in Call of Duty 4, AUG HBAR, is an Austrian assault rifle originally designed in the 1970s. The Armee Universal Gewehr ("universal army rifle"), was adopted by Austrian forces in 1977. It has since become the standard small firearm for the Austrian Bundesheer and national police units.

Call of Duty: Modern Warfare 2
The AUG HBAR is never actually seen equipped by the player in either of the singleplayer or multiplayer clips so far, but it has been seen as an option to pick up off the ground.