There's a couple of companies that make them, but Harrt's is the best, IMHO. All it is is a steel tube filled with mercury, suspended in which are stainless steel ball bearings. The tube replaces your current guide rod (and has a better spring on it, for that matter). When you fire, the balls move within the mercury and soak up lots and lots of muzzle flip.
Costs about 90 bucks retail, but you might be able to get it from Brownell's for much less. Gun dealers want to make you think there's some kind of smithing involved, but there's not.
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