The military 30-06 is loaded to a specific spec and power range, that the M1, and other guns in service in that caliber, were designed to operate in.
The commercial stuff is loaded in a variety of loads, some using heavier bullets and slower burning powders that are outside the M1's designed operating range, which may cause damage to the gun.
“The enemy is anybody who's going to get you killed, no matter which side he is on.”
― Joseph Heller, Catch-22
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