JT: lots of available aftermarket vernier aperture sights available for the No. 1 rifle. These increase the sight radius and you can alter the aperture size on many to suit you. They are fun to shoot with and look correct on the No. 1- in fact they are correct with certain types actually having been used by "snipers" in WW1. These are getting pricier but still can be had for a lot less than a scope/ mount. Also, don't discount the standard military sight. If your rifle is set up properly you may be surprised how easy it is to hit targets at 4 or 5 hundred yards. Conversely, if you can't see signs of accuracy potential with the stock sight it may reflect problems with fitting of the forend, etc, that won't be cured with a scope or vernier sight. They are wonderful rifles- you'll have several pretty soon I would guess!
Ridolpho