One of the guys in a group that I am part of has an Armalite AR-50 and the AWC Turbodyne. It does a good job of taming the report, but the felt recoil is higher with the can than with the factory brake.

Having never shot a Barrett 99, I don't know how the Barrett brake compares, but I have heard in the past that the AR-50 brake is more effective than most other .50BMG brakes, so the increase in recoil on the 99 might be less.