There had been some work starting before WWII to modify the M1 Garand to accept a detachable box magazine in place of the en block clips, and to allow the possibility of select fire. Nothing really happened until after the war, when John Garand came up with the T20, which adapted his original design to accept the detachable magazines from the BAR. As development work continued, Earle Harvey and others at Springfield Armory came up with a different design, the T25, using a shortened version of the .30-06, which ended up becoming the .308/7.62x51. More work resulted in the T44, which eventually became the M14. So the answer to the question is that there was indeed a US military rifle in .30-06 with a detachable magazine (T20), but it was never issued.
Ken