Your Krag's stock is a model 1899 carbine stock, that someone defaced by putting on the rubber butt-pad. Your stock lacked sling-swivels. A hunter improvised some.

Your Krag is chambered for the U.S. .30-40 cartridge, unless someone re-chambered it - (unlikely).

Sometimes Krag serial numbers are very deeply stamped and it is easy to misread digits. 3s can look like 8s. 6s can look like 8s. 5s, 9s and 8s can be confused.

Highest U.S. Krag serial numbers are in the 480K range.

Your number is in 357,XXX range. Your pictures are poor in clarity. A magnifying glass and good lighting should help you decipher your number.