I have a Model 12 WS1 which flares .020 after the choke which is .006. But I have measured several others WS1 which went down to .003-4. I expect yours are original. Winchester guns of this era were surprisingly light choked. I have had full choked guns which only had .030 choke in them and they threw very tight patterns.
Mine is from 1947 and measures .008" before the flare. The point of maximum constriction is a good bit closer to the muzzle than 3" (Crossman) or 2 1/4" (Ithaca drawing). They do vary considerably.
Left is WS-2 and measures .015". I have no idea nor have I heard a satisfactory explanation as to why Winchester considered .015" applicable to the game of Skeet.
The gun is choked perfectly for doubles from 4. If all you shot was doubles from 4, you would have as they advertised "Your Gun for Skeet".
Since reaming on my original Model 21 seems unwise no matter how silly this "Skeet gun" is choked, I use a spreader in the left barrel for doubles everywhere except 4.
Beretta also uses the constriction/flare profile for their interchangeable chokes marked 'Skeet'.
