I have a Lefever 10 gauge rod cocker in the 10K SN range which has a 3" chamber in it. Prior to WWI most American makers would chamber a gun to most an length desired, mainly in 1/8" steps from 2 /12" to 3 1/4", with 2 9/16" thrown in to boot. 8 gauge was available longer than the 3 1/4" length. I am not sure if there were any 3 1/2" tens made prior to the Western Arms/Ithaca NID connection or not, but if so they would not have been for "Magnum" loads just longer wad columns with standard loads as was the early 3" 12 & 20 gauges & possibly even some 16s.
