From the milsurps search box; Sorry Bindi they came in 4 lengths so there is 1 1/2"s difference between the Long & the Bantam Butts for the MkIII so the 1914 BSA could have a Bantam & his 1944 a Long giving the impression of a shorter barrel pics would help. The barrel length in the MkIII's was always 25.2" the long toms were longer barreled with an entirely different stocking up.

The Butt lengths & names are: 12 3/4" (Long), 12 1/4" (Regular), 11 3/4" (Short) and 11 1/4" (Bantam) for the MKIII