Here's a question - is the flare an integral part of Winchester's skeet choke, or is it just the hallmark of handworked chokes (aka manufacturing tolerances)?

I have a M12 skeet that tapers (v slightly) all the way to the muzzle. I also have a very original F&F M21 Trap with 32 points of choke in each tube, but one barrel flares 7 mils.

What I have found over the years is that is is very unusual to find identical choke profiles in two barrels from the same manufacturers.