Hope this explains my reference to W & C Scott.
W & C Scott was, as you are probable aware, the fine gun making division Of Webley & Scott and would have been be the logical business location to make the replacement barrels for the Atkin.
Based on the proof marks, most guns of that era were using steel barrels. At that time Scotts would still have had access To Damascus barrel blanks, suitable for making the replacement barrels to matched the Atkin originals. Hence the proof marks appear to be out of historical sequence!.
You may recall that in recent years W.W.Greener made several guns fitted with damascus barrels, using old barrel blanks from their Inventory. Following passing proof test, these guns would have the proof marks of the day applied without any regard to the age of the Damascus barrels.
Thanks. We're on the same sheet of music. The chamber length mark (1925 rules of proof) on new Damascus barrels had me scratching my head.