I don't have battlefield experience on human opponents with either round (gratefully), but in my training days there were demonstrable differences. My opinion has been reinforced by the experience of soldiers recently returning from Afghanistan, including my son.
On the ranges, for sure, but that may also have been down to differences in the rifles. Older rifles often (at least in theory) are design for accuracy at long ranges, and aren't all that distinguishable from target rifles. More modern rifles, though (I'm thinking of the M4/M16, SA80 and so on) are consciously designed with the understanding that a soldier's work requires far more than just accurate shooting - in fact, that accurate shooting is often a secondary concern. For example, something like an SMLE might have a long barrel for accuracy, while an SA80 has quite a short one, because carrying the rifle around and using it in close environments (such as getting out of a vehicle or aircraft, or moving around an urban environment) is easier with the latter. Bear in mind the precision you have in range shooting - a good shot puts down two-minute groups, which means all of the bullets land within one part in thirty of a degree - and then consider that the lovely body-position and regulated breathing goes to pot when you're in combat.
Best of luck to Vogtmurr mark 2, by the way.
There are long lines of sight in many engagements there which snipers have taken full advantage of.
Those long lines of sight only really exist if you're lying in wait with a telescopic sight. A normal patrol, scanning its arcs, probably won't see a cammed-up enemy beyond 400m. Even then, very few soldiers, firing with iron sights and only their arms for support, will be able to hit a human-sized target at (say) 800 yards within ten shots, even if said target is simply standing still in full view.
But even at ranges <300m, many Taliban fighters have been able to run wounded with multiple 5.56 shots. They may not know they are already dying but what good is that if they have time to trigger an IED or communicate/warn their fellows ? (Its also not very humane, if that should be a consideration).
While I don't doubt that the occasional one has, that's
very rare indeed and they're always in that sort of case very poorly placed shots. As BF said, that will happen with nearly any round.
Wind is also a major factor in Afghanistan, in Vietnam I would think it would have been foliage. I guarantee I can put 7.62mm rounds through trees (and they are not yew) that a 5.56mm will not. My perception is that 5.56 is also more subject to deflection.
Perhaps I exaggerated slightly, but the point stands. 5.56 is good enough for pretty much any cover or protection that the enemy might be wearing; 7.62 is better but we don't actually need that degree of penetration
at the cost of the increased weight, recoil and physical size. It's all a compromise, really.
The concern, incidentally, is not so much the weight of the bullet per se, but the energy that it has when it flies - which is a factor of its mass and the square of its velocity. In other words, a bullet with half the mass but twice the velocity hits four times as hard. Similarly, wind deflection is a factor of the bullet's weight, its ballistic profile (a larger round has a bigger surface area to be acted upon), and the amount of time that it's in the wind. In other words, you often find that a small bullet moving very fast will be affected less by wind than a large bullet moving relatively slowly.
5.56 in the loads that the military use is more subject to deflection, but that's not the fault of the bullet - it's to do with how much and what sort of powder is behind it.
In general using it fully automatic is bad. You waste the ammo capacity advantage and can't hit anything after teh first couple rounds. Burt fire is where it has always been. Since the earliest machneguns, sustained fire was not good. Instead firing 3 round bursts gets lots of round on target fast without completely ruining your accuracy.
Well, machine-gunners don't do that because firing belts and belts of ammunition will overheat and wear out the barrel, but for ordinary riflemen, in general, a few shots fired accurately work better (even for suppression) than many shots fired inaccurately. It's relatively easy for a moderately experienced soldier to tell when enemy fire is effective.
I like burst of two to four rounds, in general. The one thing I'd say sustained fire really has going for it is at close ranges, whether it's as a show of force - if you can put ten rounds through a window when the enemy pops up, he's going to get his head down sharpish and perhaps think that there are more of you than there are - or for when the enemy appears within bayonet range and you want to be certain about it. There's something very comforting about just squeezing and knowing that you're putting out an unholy amount of firepower before he can react.
Hell, the standard US rifles are not mechanically capable of fully automatic fire.
Which I consider a design fault - see above- but understandable considering that they're designed to be suitable for troops who aren't as well-trained as the British; conscripts in Vietnam for example. That said, including automatic fire with a 7.62 rifle is probably also a design fault.
Once again there are tradeoffs between burst and full auto and whether automatic is available or not.
I would always say that if the training's available, teaching people to operate a fully-automatic weapon in bursts is the best approach.
And why would a bigger bullet do much better? I've already explained how shot placement is paramount. If you don't hit a vital part of the body, then you're not going to get guaranteed immediate incapacitation. It's as true for any caliber until you get into the ridiculously large stuff.
Well, not quite true. 7.62 is far better at salvaging bad hits - for example, shooting a drugged-up Liberian in the leg, which soldiers using the SA80 complained didn't always stop the man from attacking - than 5.56, because it causes enough damage that pain threshold isn't a factor - that is, the bottom half of his shin-bone stops being attached to the top! But you're right, it's far from perfect, and if you hit someone in a vital organ with anything they'll go down.
That said, the 5.56 round is designed to work more through a phenomenon called hydrostatic shock, in which a faster (but lighter) round creates pressure waves in the body as it hits, which cause damage such as internal bleeding and brain haemorrhaging at a relatively long distance from the entry wound. Not particularly pleasant, but effective - it's essentially a scaled-down version of what happens when you fire a .50 HMG in the general vicinity of a target and still 'hit' it, because the pressure wave generated by the round is lethal even if the round itself misses.
