The Krag-Jorgensen rifle was short-lived in US military service, despite being a major step forward in technology. The M1892 Krag rifle replaced the Trapdoor Springfield, and was the first generally-issued repeating rifle and also the first to use smokeless powder. After some brief use in the Spanish and Phillippine conflicts, it would be replaced by the 1903 Springfield rifle.
You can find a 1917 original manual for the 1898 Krag rifle and 1899 Krag carbine in the Original Manuals section of the Vault:
(1917) US Model 1898/1899 Krag Manual (English)