Welcome to ShotgunWorld, kd5exp
. You can learn about the King Armory KA-1212 muzzle brake which installs without threads outside the barrel here
. Send them your rifled barrel for a professional installation, or buy the part and DIY. Order the King Armory KA-1212 here
, after you have measured the outer diameter of your rifled barrel. The King Armory page on Facebook is here
Now, let me ask, why do you think that a muzzle brake on a rifled barrel is sensible? A shotgun is not a rifle. A hunter might use a rifled barrel on his shotgun when hunting in those few states with restrictions on rifles, but if he does, he will shoot sabots and probably have a nice scope too. A hunter would have near perfect target acquisition on the first shot, and he would have no need for a muzzle brake to reduce muzzle rise, allowing a good secondary shot. Could you please explain your situation, sir?