The operating theory is that the holes in the brake divert some of the exiting powder gas toward the rear, which reduces the forward jet thrust of the gas and even exerts a forward push on the muzzle.
Some work.
Some don't.
In fact, some brakes actually increase the effective recoil by reducing the rise of the muzzle so that all the exiting gas pushes the rifle straight back.
Many degrade accuracy. In one extensive test years ago, every brake tested made the barrel shoot larger groups.
Most make the muzzle blast louder.
