By the 1950s, the Pedersen needs quite a few improvements to make it up to spec. Ammunition design made quite the number of developments around that time. Now, it would've been an amazing and modern calibre for the M1 Garand, 20 years earlier, hadn't it not been cancelled for a variety of political and economic reasons.Either that or the Pederson .276. Having an actual intermediate cartridge would mitigate many of the issues with the M14, and it'd be more likely to continue on.
And that bastard MacArthur!