Note that with nominal bore sizes of .410" & .526" for the .410 & 32ga rspectfully 12mm & 14mm are not true bore sizes for these guns. 12mm = .472" which is approximately case dia for the .410. I do not have at hand chamber specs for a 32ga but with 14mm = .551", .025" larger than bore dia, it is doubtful if any part of a 32ga measured to 14mm, unless they were all originally chambered for all brass sheels & thus had smaller chambers in relation to bore dia.
I seem to recall the .410 also being listed at times as a 36ga which has a bore of .506". "True .410 bore size are 10.4mm or 67.49 gauge.
Note that I am fully aware that the makers listed them in these alternate sizes, but they were simply nominal names bearing no relationship to actual sizes.
