I've not seen a hint such a weapon is in current game.
According to Google, The All Seeing and All Knowing, no such beast exists.
Sad face.
I know this will be rectified in coming months via mod community.
In the meantime, the 44 (mag I think going from damage range) is making me smile.
The hunting rifle that is the most iconic sniper rifle can be upgraded to .50 BMG for a very nice damage boost. that will free up your .308 rounds for other applications.