If you stray too far from 7.62 NATO standards regarding bullet weight and pressure, you can get into durability, reliability, and accuracy issues. The M-14 was designed for 150 gr bullets, with military powders tailored to have the correct pressure characteristics at the gas port. The twist in the M-14 barrels likes 168 gr bullets for excellent accuracy. Those who choose heavier bullets at high velocity, for hunting or for long range target shooting, will have to be aware that recoil from these heavier bullets can do significant damage to the M-14 rifle. Those who go too light, either in bullets or in powder, may find the gas left over at the port may not have enough power to operate the mechanism reliably and consistently. That being said, I have tested a few M-14 rifles with the sabot loaded Remington .223 55 Gr Accelerators, and this makes for a reliable shooting load, with no recoil, that may be accurate in your individual M-14. As usual, with individual opinions and experience, your personal mileage may vary.
The M-14 rifle is incredibly sensitive to variations in ammunition, and some loads may shoot MOA out of your individual rifle, while others are closer to hour of angle. Best advice I can give on ammunition, is to try as many different brands, weights, and types of ammo, 7.62 NATO Ball and .308 Winchester, to find what your individual rifle likes. Then buy a case of it.
