[quote=@Sophrus]
[@Zaresto]

Oookay... Well fine it's an anti material rifle. I didn't realize we where going to be that stingy.
[/quote]

It can be the Oliver Anti-Materiel Rifle, it's used by the NCR Sniper at Hoover Dam and uses .50 MG. In New Vegas it's an unobtainable item, but can be gained through console commands on the PC.