There are a few factors. The first is ammo. Better ammo gets better results in both distance and "put down" power. The second is barrel length. Longer barrels usually generate better muzzel velocity and have more energy at longer rangers. Lastly is optics. There are pleanty of guys that can put all their hits on a man sized at 750+yds with iron sites. The ACOG is regulated to shoot out to 600m. But, better optics usually yeild better results. As a Designated Defensive Marksman attached to a sniper team, I used a modified m16, the MK-12, with a 20" barrel and 1/7 twist shooting 77gr Sierra Match King HPBT with a really nice Nikon scope. I could hit a 6" target at 500m semi rapid fire, and I was not a fully trained sniper. When you use better equiptment, you get better results. A lot of the Navy Specialized units are breaking out the old M-14 for long ranger work. The Marines are using the MK-11, an AR platform chambered for .308 that has had EXCELLENT restults. Obviously, the bolt actions are preferred for supreme accuracy, but the ARs do well when "combat accuracy" is good enough.
As a bit of an aside, and I am not trying to start a flame war, but most of the complaints about the liminted range of the M-16/M-4 comes from the Army; after all, there are more of them. The Army only trains its soldiers to the 300yd standard as a general rule. Yes, there are many that can do better, but that is the Army standard. Additionally, I have seen AimPoint optics, which have no magnification, riding atop most USA rifles. The Marines on the other hand, train to shoot out to 500yds in Boot Camp, and infantry sustainment training includes shooting to 600m with ACOGs, which is what tops almost every USMC rifle. These are only my observations, but as a general rule, the Marines just shoot better. They are a rifle culture.
As a bit of an aside, and I am not trying to start a flame war, but most of the complaints about the liminted range of the M-16/M-4 comes from the Army; after all, there are more of them. The Army only trains its soldiers to the 300yd standard as a general rule. Yes, there are many that can do better, but that is the Army standard. Additionally, I have seen AimPoint optics, which have no magnification, riding atop most USA rifles. The Marines on the other hand, train to shoot out to 500yds in Boot Camp, and infantry sustainment training includes shooting to 600m with ACOGs, which is what tops almost every USMC rifle. These are only my observations, but as a general rule, the Marines just shoot better. They are a rifle culture.
