As a former Infantryman, I was never issued an M14. However, I did purchase an M1A and LOVE the rifle. There are bullpup frames that will accept the M14 barrel and trigger group. The 7.62 x 51 is far superior in reach and punch than the 5.56. Stand off distance is also very important. During Vietnam, the jungle reduced the average sight / stand off distance to a couple dozen yards. In desert and arctic warfare, the engagement ranges are much farther and need a heavier round with more powder to reach out to 600 yards.