Huh? There were reports of GI's firing 7.7x58 Japanese out of M1903 rifles in WWII (yes, it will work, but not the reverse), but how did NATO, which was not founded until 1949, solve some kind of ammo supply problem in the Pacific in WWII?
I obviously don't know what tests the French conducted (and I doubt anyone outside MAS does, either) but I think they probably tried all the NATO standard ammo before deciding only steel case would work. The question is why the higher ups would approve such a "solution" instead of adopting another rifle or sending the designers back to the drawing board.
French relations with NATO have always been, well, interesting. At one point, the French politicians would not even agree to joint maneuvers, which their military considered essential. The result was that the British, Americans and Germans would set up an exercise to begin, say, at 0700 on such-and-such a date. The three forces would be in position before that, but there would be a gap between them. At 0600, a French unit, which just happened to be in the area carrying out totally independent exercises, would move into the gap. By pure coincidence, of course, the French wanted to carry out their own maneuvers in that same area, and again by pure coincidence, their actions conformed to those of the other units.
Silly games. I wonder if the Soviets let their Warsaw pact allies indulge in such childish nonsense.
Jim