It functions very much the same as the standard anti-materiel rifle with increased damage, health and no spread but decreased critical hit damage bonus. It is used by an NCR sniper at Hoover Dam during the final battle, if the player is working for Caesar's Legion. However, the player not only needs to be serving the Legion to access Oliver's compound, but they need to fail the Speech checks against General Oliver to explore the cell in which the sniper holding this weapon is found.
The Oliver anti-materiel rifle can only be obtained via console commands. It will NOT be obtainable from the sniper wielding it even if killed, as he will drop a normal anti-materiel rifle, and his corpse will still be holding this one.
It will appear in the Pip-boy as "anti-materiel rifle", but it cannot be stored or picked up if dropped; this is due to it being marked "non-playable."
With the Better Criticals perk, this weapon actually does less damage than the standard anti-materiel rifle as the critical damage bonus of this weapon is significantly less than that of the standard rifle.