The only evidence of its existence lies in the game's files, which when accessed through modding leave an unfinished gun which takes the appearance of the Dragunov, makes similar noise as the Barrett .50cal and has a five round magazine, as well as a very low firecap. It also has less recoil than the Barrett .50cal and does not make any noise when reloading. Note that there is also no ammo counter.
The AW-50 was probably cut because the developers thought two .50 caliber rifles, or 3 bolt-action rifles were unnecessary.
In game files, it is possible to find two files, one texture and one menu icon, however, both are completely black and small-sized. In Call of Duty: Modern Warfare 2, only menu icon file is found; again; it is small-sized and completely black.
In the game files, it shows a lack of the usual 1.5x multipliers on sniper rifles and the maximum damage, as well as the minimum damage, is 100, indicating that it may have been cut early in development.
The AW-50 has its own sound effects, even its own firing sound effect, which differs from the Barrett's as it is a slightly higher pitched sound. Having its own sound effects which were never implemented in the soundmap, this is the reason it makes no sounds while reloading.
The seemingly large firecap is due to the long rechamber time that would have been in place due to the bolt-action nature of the AW-50.