One additional fact supporting this is that the .276 caliber round that the T3E2 used, and the .276 caliber that would have eventually been adopted had MacArthur’s edict never happened, were not the same! The round used in the T3E2 Garand rifle was a well-tapered cartridge with a .447″ cartridge base, thinner than the .473″ base of the .30-06 Springfield round. However, this round did not meet the performance specifications desired by the US Army when loaded with every kind of propellant the Army wanted available, and as a result the specification was changed to the larger .276 T2 cartridge, which utilized a modified version of the .30-06’s .473″ case head, with about the same overall length as the previous .276 cartridge (2.85″). This cartridge was about the same size and weight as the more modern 7mm-08 Remington round based on the .308 Winchester (the civilian offshoot of the .30 Light Rifle, which became 7.62 NATO), and it was this larger T2 round that would have been adopted as the .276 caliber, had that come to pass. In other words, had the .30 caliber not won the day, the US would have adopted a round very similar in size, weight, and capability to the later 7.62 NATO. It seems likely to me that had the .276’s adoption gone through, it would have precluded the .30 Light Rifle cartridge program, rather than the .223 caliber project. In this alternate timeline, maybe today the US Army would be using 5.56mm NATO in conjunction with a venerable, well-tapered “7mm NATO” based on the .276 T2!