I would like to see photos but I think the D means damascus. (T was used for twist.) The R means it went back to the factory for some sort of repair or, perhaps in this case, a new set of barrels. It is too bad that that era records are missing. The story I got was they were destroyed in an office fire.
Here is a Grade 3. Does your D look similar?

Last edited by Walter C. Snyder; 12/17/12 10:42 PM.
Walter c. Snyder