The Accuracy International AW50 appears as the “Victus XMR”; it is available in Season 1 under the Imperatorium platform. It is worth noting that the AW50 was planned for the original Modern Warfare game, but only its code and firing sound (which sounds similar to the M82A1 in that game) are left as the weapon was scrapped, and it wasn’t added to the Call of Duty series proper until MWII.
Accuracy International AW50 (latest version with fluted barrel and redesigned muzzle brake) – .50 BMG
The AW50 in the loadout screen. The lower end of the thumbhole stock lacks the cutout to fold, despite the hinge on the upper half.