Interestingly, several of our makers started doing that style choke when they brought out "Skeet" guns in the 1930s. Winchester had their WS 1. The Remington SKEET choke found on their Model 31 pump and "Sportsman" auto loaders had about .005" then a flare to the muzzle. Savage's Skeet Cylinder in the right barrel of their Ansley H. Fox skeet guns were similar. The ones I've measured have bores of .728" with choke to .723" 1-inch from the muzzle, the flare .017" to a muzzle diameter .740". I just measured a Remington Model 31 barrel with a bore of .726". at two inches from muzzle choked down to .720" then flares to .730" at the muzzle.