I recently acquired a Pre War Model 21.
1939 20 gauge, Skeet grade, 28" WS1/WS2,
90%+ original condition and a skosh more DAH than is typical on some Model 21's.
I shot it for the first time this past Saturday. 25 - 25 - 24, dropping high 5. It's a keeper.

[Linked Image from i.imgur.com]

[Linked Image from i.imgur.com]

While still at the gun club with the help of a fellow shooter and a gauge we measured the chokes.
WS2, .610 bore with 12 points of constriction.
WS1, .610 bore with 2 points of constriction and then a flare of 28 points negative choke.
Shocking but vaguely familiar. Some one declared that someone had FU(KED with the choke.
Jack surmised that some mid century philistine with little or no regard for the sanctity of Winchester 21 barrels
had opened the right barrel trying to garner an extra clay at Skeet or some imagined advantage in the uplands.
I thought differently and uncharacteristically held my tongue. Yah, right.

That afternoon I contacted the best gunsmith west of the Atlantic and learned that this choke was pure Winchester.
Terminal flare well past Cylinder is what Winchester research developed for the ultimate 20 yard shot.

I searched the internet for a diagram depicting this proprietary choke but came up with nothing.
Does anyone have an image of a WS1 choke that shows this flare?
Thank you.