MWD
Your Model-51 was produced in 1926. If you look on the left side, on the front of the trigger guard, you should see two letters. The second should be a "T" for 1926, the first will be the code for the month. See the page on this site (http://www.remingtonsociety.com/rsa/que ... arrelcodes) that will give you the code information. Your pistol was 1 of 4,617 produced in 1926.
Chuck D