Here are a couple pics of the Painkiller muzzle brakes that have been mentioned already.
These are the unfinished brakes just finished being CNC machined. Finished brakes have much different look. Here are examples of the large 5 port PK muzzle brake suitable for muzzle diameters from 0.800" to around 1.000" diameter. The medium size 3 port brake are usible on muzzle diameters from around 0.660" up to around 0.900". The small 3 port PK is for muzzle diameters from .590" up to 0.750".
Thread specs are 3/4x28 tpi, 5/8x28 tpi and 9/16x28 tpi.
All three sizes should be in shop within a week or so.