Never cease to have questions..... the Poyer book states on page 168 that "the model 1901 carbine rear sight was originally assembled to all Model 1899 carbines after serial #345,000....."  That begs the question of what rear sight was used prior to serial number 345,000?  Earlier he states that the 1898 rear sight was added to 1899 carbines between serial numbers 242,000 and 285,000.  So what was used before on the 1899 carbines.  The one I have has a serial number of 235,xxx.  Thank you