Doomed Long Branch Sniper Reborn

[Seaspriter]

That is an indication that your butt stock was originally fitted to British No4T serial # 39515 as they stamped the rifle serial number protected inside the butt socket and the scope serial in the open.

Thanks LE. Your insight led me to use a very large magnifying glass on the underside of the wrist, where (almost too difficult to spot with the naked eye and too difficult to photograph, but still distinguishable) were the tell-tale marks:
SL
N
74
(Sykes Limited, walnut stock).
So, your assessment is probably quite right -- my guess is the Sniper was damaged in combat, and a new butt (and possibly another scope) fitted to the rifle (or possibly salvaged from another damaged British sniper).