The Halbek Device was a clamp-on muzzle brake designed by two Rhodesians, Douglas Hall and Marthinus Bekker. It was patented in Rhodesia in 1977 and in the US in 1980, and manufactured in small numbers for the Rhodesian military. I have seen these occasionally, and doubt they are actually very effective. But during a filming trip to South Africa I had a chance to actually try one on a select-fire R1 FAL, complete with high speed camera to find out for sure. So, let's see what they really do...