44spl mentioned in an early thread that it should have a Star guaged barrel. To me, it reeaaallly looks like a Star stamp on the barrel between the 1:00 and 2:00 positions. This is not normal however, to my knowledge all Star stamps were placed at the 6:00 position. I will attach a link to a photo of a Star guaged stamp. You may have to copy and paste in your browser to get it to connect. In the meantime, you also asked (in another thread) what were the best loads for the ol' girl. 168gr, Sierra match kings W/ 47 gr. IMR 4895, you won't be disappointed.
http://vishooter.home.att.net/m1903/mzl_str.jpg
Also, on the m1903.com page left column is a Manufacutre Dates link. It takes you to the VI Shooter page, it's very valuable. Let me know if the stamp is right and the loads work.