Does yours have the little block arrangement in one corner for the Bolt? Can't see it on the pics.
This one also has the Alex Martin legend in the same location and same font as yours.
Printable View
Very interesting. Always thought that the early sniper rifles needed an individual chest but never saw one. The first L42's on trials at Warminster came in No15 chests - with the muzzle end of the box knocked out to accommodate the longer rifle.
Yes the bolt block in the corner remains, nice to see one in its original condition!