The 1901 sight is the sight most commonly encountered on 1899 carbines. Whether or not it was fitted new depends on the serial number.

The sight first fitted to the earliest 1899s was the M1898C. This was graduated for the "hot" 2200fps ammo, and a few cracked bolt lugs showed up. That sight was withdrawn, and a brief reversion to the M1896C sight occurred.

Somewhat later, the M1901C sight began to be fitted to new production; later, it was retrofitted to earlier M1899, and restocked M1898, carbines as well.

The serial number would tell us a lot here.