Sure, Drewbie-- between the Nickel Steel WRA used from about 1896 until the Winchester Proof Steel came on to the market in aprox. 1931 (same year the M21 was on the market) WRA had the Fubared Stainless Steel options for some of its rifle and shotgun offerings- The M54 rifle and the M12 shotgun. One of their greatest advertising blunders was the ils. of 2 deer hunters carrying a deceased buck deer on a pole in the rain-- "No need to clean your rifle right after the hunt" etc. BS. I clean whatever weapon I happen to be hunting with that day, whether I fire it or not. Old USMC mantra--
I am NOT by any means a metallurgist but as a life-long welder (ferrous and non-ferrous metals, TIG, MIG and SMAW) all positions, I know how to spark test ferrous metals. WPS is basically AISI 4140- Nickel based, with Chromium and Molybedendum as additives-- I have in my gun parts inventory, a 12 gauge 30" full M1912 barrel section from a muzzle obstructed bursting. As soon as I obtain a section from a post 1931 M12 marked WPS, I'll spark test them- using a clean medium grit wheel, to avoid contamination of the exemplars.
I believe WPS was a ploy used by WRA to overcome their marketing FUBAR with the U S Steel supplied Stainless barrels- see the Madis book on the M12 for more details, if you will.
You are, obviously, a highly educated person-I am not. But I daresay I was one of the handful of welders working the trade for many years (mainly power plant code welding on stainless piping systems) that was also a member of the AWS- and read each monthly issue religiously. RWTF