Originally Posted by
muffett.2008
There are allways explanations, only one of them can be correct and, until proven to be accurate, there will always be doubt.
As the only parts you have shown other than the barrel of early vintage is the rear sight, which has the BSA marks which, if considered as inspection marks, cover a time frame from 1861-1960's, or if considered a production mark would be the 1941-1944 time frame, so I can only go on what I see.
Question... did Ian S. physically inspect this firearm? Were checks done to ensure the barrel Knox was fully rounded bar the flat to ensure it had not been altered? Was it possible that actions were sent to Britain, where this change was more likely to have occurred?