The ammunition for the M14 and its copies (M1A, M14SA, M14S, etc) - just like the M1 Garand before it - was designed to function within a relatively narrow band of bullet weights, velocities, and pressures. This is primarily due to the gas system's specific design (porting, cylinder volume, piston weight, recoil spring tension, and weight of the oprod). Too much force acting on the bolt's roller and lug to unlock it can be detrimental as is the rearward motion/velocity of the bolt. There are multiple considerations in the basic design and a self-loading rifle needs to stay within those design parameters.
The weight of the projectile, the burning rate of the powder, and its pressure curve are important and need to be managed, controlled, and observed.
Some commercial ".308 Winchester" sporting ammo can easily exceed the design pressure of 50K psi. (even up to 60K psi. or more). Some ammo will not develop proper port pressure - or will exceed proper port pressure. To keep your system running smooth and long, heed the original specs. Exceeding them can be hard on the equipment.
"M14's" are robust weapons but you cannot just feed one "anything" a bolt gun may tolerate just because a cartridge will fit in its chamber. HTH