I suppose it should be "calibre"...
In a comment to my post "Philosophical differances", recent recipient of a Tamalanche!, the subject of the US overriding the UK's desire for a smaller caliber for battle rifles came up in comments.
THE .256 BRITISH: A LOST OPPORTUNITY tells that tale.
According to the Wikipedia article on the M1 Garand rifle, the minimum caliber that was specified for the replacement for the M1903 Springfield rifle was .256--!--, but a .276 was settled on--until Chief of Staff General Douglas MacArthur directed that a .30 (.30-'06) rifle be pursued, "in part because there were extensive existing stocks of .30 M1 ball ammunition."
My first gun, paid off @ $20 dollars a week until I turned 18 and could pick it up at Neumann's Gun Shop, was an M1 Garand.
The push to replace the M1911 .45ACP pistol with a 9mm in US Service was underway when I enlisted in 1980; testing was going on when I arrived at Ft Ord, CA, and double-dog dared the Army to ditch perfection1 with some Euro-weenie poodle-shooter, and purchased myself a Colt Combat Commander.
I'd say "that turned out well" in a snarky manner, but, y'know, it did: I never did get used to the bulky, blocky Italian beast they replaced it with, but I still enjoy shooting John Moses Browning's (pbuh) masterpiece. (Although, considering the sheer magnitude of his oeuvre, can we really say that?)
I may have told this story: As we were deactivating a unit in Korea, we had an ammo bunker full of .45 ACP to dispose of, and no units in Korea with .45s. All us NCOs were offered the opportunity to go to the range and, um, dispose of it in the proper manner. There (IIRC) 4 or 5 of us, sharing the range with a company of MPs who had just replaced their .45s with M9s. I qualified Expert, as did most if not all my colleagues.
The MPs all bolo'd.
Worse, 5 years later I was attempting to qualify with an M9 at the exact same range, and so did I.2
1. Yeah, I know. Some of you agree whole-heartedly, and some of you are clutching your pearls and gasping prayers to Saint Gaston.
2. In my defense, in the interval, I had managed to qualify with an M9 during two other assignments; the Army had at least three different courses of fire for the pistol.