i was online and found this
http://www.tactilite.com/models/view-all-products.html
The Tactilite T2 is a .50 BMG upper that features a side-mounted, 5-round magazine made by Accuracy International.
$2,398.00
-AND-
http://www.bohicaarms.com/far50_features.html
Starting at only $1,295.00 (24" 50 BMG UPPER)