Have you checked the United States - Milsurp Knowledge Library (click here)?

There are a pair of "all correct" 30-40 Krags (rifle and carbine) for comparison.

Model 1898 Krag (Caliber 30-40) Rifle (click here)

Model 1899 Krag (Caliber 30-40) Carbine (click here)

Here's pics from the carbine photo montage of the rear sight that should be marked for carbines....

(Click PIC to Enlarge)(Click PIC to Enlarge)

Does yours have the small "c" on the side as shown in the pic above?

Regards,
Doug