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The US M1 Rifle went through a lot of iterating. The trials for the rifle were pretty complex, involving a lot of contestants, such as John Garand, John Pedersen, and Colonel John T. Thompson, to bring up more notable names.
The program was actually largely focused on the new and proposed .276 Pedersen rifle cartridge, a slightly smaller one which would provide comparable exterior ballistics to the .30-06 M2 Ball cartridge already in use, but with less recoil, weight, and bulk. Compare it to 6.5mm Swedish, 6.5mm Arisaka, etc. There was a lot of support around this cartridge, because it was actually pretty good looking on paper, but it would ultimately be vetoed by General Douglas MacArthur, who in one sense was a deranged and bloodthirsty lunatic for completely different and unrelated reasons, but who was also totally right about the issue.
To start with, the US Army didn't actually have all that much budget at the time, while it still had massive stockpiles of M2 Ball from WW1 which still worked perfectly fine. Adopting a .276 infantry rifle meant a gun which was no longer compatible with this stockpile, and it would also mean that you no longer used the same ammunition for rifles and machineguns, which in those days would be a pretty considerable drawback in logistics, unless you wanted to replace or adapt those to the new cartridge, which would be a pretty costly and time consuming proposition.
The rifle which ends up winning the trials is of course Garand's, he was one of the contestants who had also continued developing their rifle in the .30-06 cartridge with the understanding that the .276 one may have a fuzzy future, and his was also the best by far. Pedersen's rifle (which used an almost Luger-like toggle-lock mechanism) came second, while Thompson's was actually quite awful, mostly for being based on imaginary principles of physics, ejecting spent cases with enough force that they tended to lodge themselves into nearby wood boards and fenceposts.