'jzitch' - You do have a U.S. Krag model 1901 rear sight.

Your leaf that goes to '23', (for 2,300 yards), is a carbine leaf. The rifle leaf is only marked to '20'.

Unfortunately, your eye-piece has been altered by someone's filing a 'sighting groove'. (orange oval)

A 1901 carbine sight, that is complete, will have the letter "P" stamped where I have marked green arrows.

(note - Local Boy caught my error. A "C" should be stamped where indicated by green arrows).

---