It would appear that "reverse boring"--or what we'd consider to be reverse boring today--was actually standard on Skeeters. "Regular boring right barrel choked left barrel open." So it looks like sxsman has the right definitions for O and C. The 1940 Shooters Bible also gives patterning data, 3" .410 with 9's: "Right barrel, 338 shot in 30" circle at 30 yards. Left barrel, 347 shot in 30" circle at 20 yards."