here is a paper on the M1905 sight.  It has a similiar build.

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Also, I pulled my collection of rifle sights.  Using the magic mad scientist goggles I checked to make sure my memory was not faulty.  The slides are marked with a teeny tiny C.

See modified photo.  Perhaps your sight has remnats of the mark under a bright light?

You know, Whig.  I am over by Gettysburg so if you ever need a second Krag opinion or need someone to shoot up your ammo for you I'll be there for you.  ;D

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