Interesting. Back in the 1930s, when what would eventually become the "US Rifle Caliber .30 M1" was being developed and tested, they played around with a .276 cartridge. It was ditched in favor of .30 cal due to huge stocks of ammo left over from The Great War.
I understand that Gen MacArthur nixed the .276 caliber because the US had mountains of US .30 Caliber ammo.
“Army Chief of Staff General Douglas MacArthur personally disapproved any caliber change, in part because there were extensive existing stocks of .30 M1 ball ammunition”.