Your brass sight protector is the "common" rifle muzzle cap that is highly desirable and, when you can actually find one, sells for around $70 or more. I have worked hard to find and buy a few of these over the years for my Krags. Yours has a beautiful patina which authenticates it as original. There are reproduction muzzle caps being sold which are bright yellow and look horrible but, if you can't find or afford an original one, are nice enough. They sell for around $40.

This is a copy of a picture from this KCA photos page that shows the variety of muzzle covers used for different Krags:

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