I'm resurrecting this thread having followed Eightbore's suggestion vis-a-vis the small hole gauge set. Took some time to get the "feel" down. These gauges are not calibrated, so I used a marker to scribe before withdrawing to choke section. Numbers were extremely reproducible, though. Thought I'd share the numbers - sequentially: bore, choke, maximal constriction. Guns are Win M-42s, except as noted.
1934 mod .406, .401 for .005
1933 rd bbl skeet .406, .399 for .007
1960 mod .408, .402 for .006
1947 mod .407, .401 for .006
1946 full .406, .390 for .016
1919 M-20 full .408, .392 for .016
1949 SR skeet .415, .405 for .010
1954 2.5" SR skeet .411, .400 for .011
1934 skeet rd bbl .406, .401 for .005
1937 rd bbl skeet .406, .403 for .003
M-37 full .404, .384 for .020
So that gives me a range of .404 - .415 for bore diameters among my sample.
The three prewar skeets (all round barrels) have max constriction near middle of choke section, though nowhere near the flare of a WS1.
Both postwar skeets, all my field 42s, a M-37, and a M-20 have typical taper to max constriction at end of barrel.
Also, note the greater amount of constriction in the postwar skeets vs the prewars.
Finally, here are the numbers on a Browning repro M-42 that has Briley choke tubes: bore .408. IM .394, M .397, LM .400, Skeet max constriction .400 at waist flares to .402 at muzzle (hmmm.....now where have I seen that before?).
Sam
