It is absolutely essential, GW, to get hold of the Gun Room at H&H and ask for details and pay for a letter on this double rifle.
It was not made about 1915 as the serial number puts it in the 1895 to 1905 era. My H&H double rifle is 179XX and I have the gunbook notes dating it to 1904 so I'd guess your friend's rifle is about 1900 or so.
The original caliber is not likely to have been the European 9.3x74R, nor is it likely to have been rebored from the .375 flanged nitroexpress (the magnum did not yet exist) as the .375 is larger in diameter than the 9.3 (which is .366). Might have originally been a .303 or, possibly a .400/.350. Maybe even rebarrelled. All this is just speculation until Pat Murphy or Russel Wilkins at H&H sorts it out.
Regards, Tim
