Hey Jack,
Most bulk .303 ammo is Pakistani, and is of dubious quality, but then we are not firing over the heads of our mates, and an occasional jam is not something that is life of death.
It is true that it is a puzzle as to why the US military was so slow to embrace advancements (some could argue that the aeroplane was an American invention as well, and no American aircraft were used in the war either). I think the biggest reason was because the military was controlled by elderly soldiers that wanted to keep war a game rather than admit it was serious.
I do not think we are getting too far off topic, as this is all history that is related to your Motor. With out the history, these old machines are not nearly as interesting.
Best
Gus