I was annoyed that there weren't any unique Anti-Materiel Rifles in the Vanilla game (excluding "Oliver Anti-Materiel Rifle" which has to be obtained via console commands and can't be unequipped once equipped), so I decided to create one. It's just a regular AMR with different stats and a new name. If anyone is willing to create a custom texture for the gun then please do!  The rifle can be found behind the locked cage in Bloodborne Cave. Happy Hunting!