I am new to this as well. My understanding is that the company became famous with the 1903 MS rifle in the 6.5X54MS caliber. If I am not mistaken, this caliber came out in 1900 & the rifle was improved in 1903. Subsequent years saw new calibers introduced such as the 8X56 in 1905(?), 9X56 in 1908(?), 9.5X57 in 1910 etc. The actions look the same to my untrained eyes. The magazine spindle is specific to each caliber of course. If you ask this question on the above linked forum you will get some expert answers.