Knew I had this somewhere, took a while to find!

John Wilkes (maker) Manton .470 NE, weight is just a breath over 11 lbs.

Distance from breech-face/ Outside diameter measured vertically:
26" (muzzles) .717
24"_ .715
22"_ .715
20"_ .717
18"_ .725
16"_ .740
14"_ .768
12"_ .803
10"_ .852
8"__ .908
6"__ .977
4"__ about 1.063
2"__ flats, not measured.

At the breech-face, flats to top of barrel is 1.250 inches
Width across breech-face (both barrels) 2.333 inches

Hope this is still usefull.