the best way to redue a crown is the brownell crowning tool kit. to polish the crown on the picture above put a marble or ball bearing of the size of a marble on the floor. put a couple of layers of 400 grit then to 1500 grit over the marble or ball bearing. place the barrels muzzle tight over the lump of emery paper, firm onto the ball bearing or marble. spin by hand the barrel making it as straight up and down as you can. the lump will stay in the muzzle and not go off cent. this is to polish after it is cut correctly. you can end up with a perfect chrome finish crown that wont have a odd fingers of gas coming off it. the high polish makes the gas ball perfect. to see it, fire the gun a night at a safe place. the fire ball should have no fingers of gas coming off the sides. a perfect ball of fire in shape. that makes for good groups. i never settle for near perfect crowns. their are many spokes of the wheel in getting good groups and a perfect crown is one of them. also when you wipe the bore between ropunds make sure you take the grease circle off of the crown also. the grease on the crown makes for a false crown and can open up your groups. clean the muzzle as well as the bore between shots.