Stevens Model 520 trench gun questions

[Keydet92]

JJM,
Very interesting. I wonder how that accounts for the mix of "P" "P." and "." marks that appear throughout this range. I know that Stevens used the "P" stamps on the tops of the barrels and receivers on the Vietnam era Model 77Es as an acceptance proof stamp, or was it hardness as well?

If you don't mind relaying your serial number, I'd like to include your mixed mark Ward's riot gun in my survey of Stevens 520/620 serial numbers and characteristics. I'm matching serial numbers to known design changes in order to accurately date all these shotguns. I've developed a history and identification guide for the Stevens Model 520/520A over on Gun Values Board (located at the link below) if you are interested or have anything to add:
http://www.gunvaluesboard.com/steven...uide-2617.html