Quote Originally Posted by tiriaq View Post
The IIIB used a front sight very much like a P14. The IIIB rear sight was a triangular shaped folder with a slide adjustment for elevation very much like a P14's. The sights are the features that distinguish a Brit. IIIB from a Cdn III. The dimensions of Ross rear sight bases are such the sights themselves may be interchanged. The rear sight was likely installed to provide more adjustments for range use. Note that your rear sight has a notch as well as a peep aperture. The sight was intended for use on a Mk.II rifle.
The Ross Mark IIIB used a front sight similar to the P-14 Enfield Rifleicon. The rear sight has been replaced with a target sight designed for the 1905 Ross Mark II as noted above. Manufactured by the Canadaicon Tool and Specialty Company, it is a Pilblad Patent Mark V sight and should be calibrated for Mark VII ammunition IF used with the short 1905 Ross Mark II Rifle, but might vary slightly because of the difference in sighting radius.
.