This is my first post on this site. I found this very interesting.
I have a 16 ga. standard grade model 21. I have no letter. One site I have checked makes me think the receiver was forged in 1935, and another site, that it was produced in 1937.
Regardless, it has 297 stamped between the barrels as well as on the back of the ejectors and the letter A in the 7 o'clock position on the right barrel. So it's possible the numbers are used to match the ejectors to the barrel assembly. The letter? Mine is a fairly early gun, so it could be a year code.
I enjoy reading and learning from this and other sites. Hope I can contribute a little.
