Is the rifle in military trim, or is it a sporter. When I see 7.7 on a gun, I think .303 or 7.7 Japaneseicon. Assuming the riflecame home from Europe, I woud guess at a post-war Britishicon sporting conversion to .303 British. If pacific theatre, it could be a gun that went to China and was rebarelled by the Japanese.

Pictures may help.