"WPS is basically AISI 4140- Nickel based, with Chromium and Molybedendum as additives"

Education comes from being willing to learn Francis; sometimes by (frequently painful wink ) experience, often times by research and reading. It is perfectly fine if you do don't wish to read the threads I linked, but it's not OK to make stuff up. You have confused 4340 with 4140.

AISI 4140 Chrome Moly
Carbon - 0.38 - 0.43%
Manganese - 0.75 - 1.0%
Nickel < .01%
Chromium - 0.8 - 1.1%
Molybdenum - 0.15 - 0.25%

AISI 4340 Chrome Moly Nickel
C - 0.38 - 0.43%
Mn - 0.6 - 0.8%
Nickel - 1.65 - 2.0%
Cr - 0.7 - 0.9%
Mo - 0.2 - 0.3%

The WPS I analyzed was non-standard 4135 with a low concentration of nickel (.09%).

The Winchester Nickel Steel was non-standard AISI 2340.

Please let us know the results of your 1931 M12 WPS barrel analysis.