Keith, thanks for your interest. The barrels on your OO would also be Armor steel as those on this Field Grade 20 ga.
The OO Grade, introduced in 1898 was offered with Armor Steel. This steel, I believe was made by an American Company and was in used until the end of the company in 1945. When Marlin bought them out and continued making L.C. Smiths, the Field Grade with Armor Steel barrels was still there and stayed until 1950 and again in 1968-71. I am sure changes were made in the steel but the only way to find out is to have as you said, samples for the different years of Armor Steel.
I would be glad to chip in and I'm sure there might be others also, to find out what the properties are in these barrels for future references.
Last edited by JDW; 01/28/12 05:46 PM.
