The below Simple Threaded Devices (STD) muzzle device is interesting for two reasons. First, it is a prototype 7.62 device that STD is currently testing. Production versions will be made from 4140 steel and nitride processed for corrosion resistance. Second, it shows an even simpler, no knurling surface treatment that they are trying.
Check out the Simple Threaded Devices website to learn more about their linear compensator line.