German GECO catalog 1937, p.54:
Amerikanische Original-Patronen
(Original American Cartridges)
...
Kal. .25-35
Diese Patrone ist auch in deutschem Fabrikat unter der Bezeichnung Kal. 6,5x52R lieferbar
(Cal. .25-35 /pictured is a specimen by Remington/
This cartridge can also be supplied in German make under the name of cal. 6.5x52R)
...
Note: translated from German by myself
Same thing again.
So in my modest opinion these two cartridges were considered practicaly the same and interchangeable up to WWII and probably decades beyond, till CIP decided, for reasons presently unknown to me, to make/declare/recognize them as two distinctly different cartridges.
"...FOR REASONS PRESENTLY UNKNOWN TO ME" is the point. Your statement above is baseless speculation. You have no reason to assume that CIP has ever changed the specifications of these cartridges which, again, is unlikely for the reasons given. The numbers don't lie. CIP has normalized these as entirely different, non-interchangeable cartridges that are clearly unsafe to mix. What we do know, for sure, is that CIP knows a LOT more about it than you do. Perhaps you should discuss it with them.
