You are incorrect about the combat load with the M-14: I carried 7 loaded magazine plus one in the weapon for 160 rounds. (also carried two to four frags and occasionally a LAW, two canteens, K-Bar, med kit and plenty of body armor.). After a certain amount of physical conditioning, anybody can. The critical part of the M-14 is that always worked, every time no matter what the conditions were and when you hit somebody, they stayed down.
As I said to an army buddy at the time when he told me that the M-14 was "too heavy for Vietnam", all he had to do was ask and we would have sent him "a big strong Marine to hold his M-14 up for him".
My point, which some didn’t get, is that the M16 from the Vietnam era isn’t the same rifle issued today. I also was comparing ammo weight, I have no idea what the amount of ammo carried with an M14 was. 160 rounds of 7.62 will weigh about the same as 350-400 5.56mm. I am young enough to have missed Vietnam, but old enough I went through college with a bunch of vets, and am well aware of the many problems it had originally. The current models are pretty well proven weapons. I appreciate your service as well, I lost a cousin (Army Airborne) in Vietnam, and a nephew in Iraq (Marine), have two brothers in law and a sister in law that are Marines, dad was in the Air Force, another nephew in the Air Force, two brothers and two uncles in law enforcement, so have more than my range time experience regarding current M4’s. The current models are pretty decent weapons, versatile, optics ready and modular as well.