I am looking for a rifle, and of course, there are far more 5.56 NATO chambered choices than any other.
What is the intended use of 5.56 NATO?
From what I read, the move from 7.62 down to 5.56 was to help out those who couldn't qualify with 7.62. Also, 5.56 is lighter, so people could carry more rounds and thus shoot more rounds.
However, the bullet is expected to tumble upon entry, otherwise it will pass through with the same amount of damage as .22LR.
Is it the reputed "wounding round"? Is 5.56 intended for soldiers only or is effective as a hunting round as well?
Should I be looking at 7.62 NATO or 7.62x39 as these rounds can be used as hunting rounds as well defensive?
Sundsvall,
Correct, the 5.56x45 mm was designed to be a lighter round for use at practical combat ranges with lower recoil and a flat trajectory. The idea wasn't all that new, the Germans and Brits had done substantial research both during and after WWII. It took a long time for the US to come around to the concept and now seems unwilling to part with it. As a hunting round, the heavier 77-80 grain rounds are adequate for game up to deer size with proper shot placement and where local laws permit the use of .223 rounds.
5.56 mm NATO is obviously a lot lighter than either 7.62x51 mm NATO or the Eastern Bloc countries then using 7.62x39 mm (deemed largely obsolete, now using a similar small caliber 5.45x39 mm round for all recent assault rifles) or 7.62x54R, so that you could carry more ammo within the same weight. It has far less recoil than 7.62x51 mm, allowed for lighter, shorter rifles to be used and was far more controllable on full auto. Round for round, it also cost less to manufacture, which may have been another important consideration.
The 5.56x45 mm use as a standardized military cartridge remains an area of controversy. While there are heavier projectiles available now (upwards of 80 grain, compared to the original 50-55 grain projectiles), 5.56/.223 Remington is heavily dependent on it's high velocity, though somewhat less so with heavier bullets.
As the bullet weight increases, the bullet must generally become longer and seat more deeply into the case. Longer bullets need more stabilization in flight and so the twist of the barrel must be increased. Original AR15s and early M16(A1) had a twist rate of 1 in 14 inches. Use of tracers, another very long round with low mass, and the new ball round designation that was used through the 80s and 90s required a faster twist than the original rifles tailored for a lighter round. As bullet weights have continued to be increased, new models of the basic design have featured faster twists to stabilize longer, heavier bullets.
5.56mm, to it's credit, can and does create substantial wounds despite it's small caliber, though this capability drops off fairly dramatically with range. The BC of the projectile isn't all that great for retaining that energy over distance. At 250 meters, most common 5.56x45 mm military rifles will be making .22 caliber holes and the bullets will tend not to fragment, bend or yaw wildly.
Some would argue the original wounding potential of the 5.56mm round have been lost, though with the rise of body armor the old round would have been far less effective. Heavier rounds with somewhat better BCs have already improved on the longer range performance, even if this has compromised some of the fragmentation potential, they still tumble fairly well due to their tail-heavy design.
The other problem is probably the rifles. The move to shorter and shorter barrels makes for less velocity at launch, further reducing the primary source of energy the 5.56mm relies upon. Heavier bullets can compensate somewhat, but these heavier rounds fired from shorter barrels affect the flat trajectory that 5.56x45 mm is known for. The net effect is while better for house to house fighting at short ranges, M4 style weapons are sacrificing velocity and energy for a shorter overall rifle, the most obvious fix being a move towards 77 grain projectiles, which has not happened yet. The bulk of the force is still using the 62 grain bullets. 79 grains is about as far as 5.56 mm can practically be pushed without changing the case to accommodate even longer bullets.
A move to bullpup rifle layout, as in France, Singapore, Britain, Austria, Australia and others would do a lot more for allowing a longer barrel while providing an even shorter package than the currently fielded M4. Fears of rounds cooking off next to the operators face appear bogus. Some of the bullpup rifles have provided added reinforcements to the receiver, added a small amount of added weight, to address that concern.
The issue of 5.56x45 mm effectiveness, while contentious, is more aggravated as the barrels lengths continue to drop or as the ranges these short rifles are asked to stretch to. The issue of shorter barrel length may be one of the primary motivations behind Special Forces' interest in moving up to the 6.8 mm SPC Remington round, or the 6.5 mm Grendel (without a large manufacturer backing them up, probably not going to happen, though I like the concept).
What made sense in the short-range jungle conflicts of 40+ years ago isn't necessarily the ideal choice for all theaters of war, indefinitely. This should be true of the venerable AR15 platform as well. Had there been more appreciation of the extensive research into the .280 British/Belgian round, the 5.56x45 mm might never have been adopted and the same could probably be said for the M16 as well. 6.8mm SPC is a close ballistic cousin to that "old" round, though 6.5mm Grendel can outperform both by a narrow margin at longer ranges (beyond 300 meters) and has more retained energy then 7.62 x 51 mm beyond about 600 meters.
By the way, not all 5.56mm or 7.62mm "NATO" rounds are exactly alike. Even when the weight of the projectiles and the pressure limits are standardized and otherwise uniform, the construction of projectiles often is not as it was not part of the details of the specification. For example, the Japanese had a 7.62x51 mm round during the 50s and early 60s that had half the recoil of the full-house rounds the US and British were using (i.e. well under the max pressure limits). The Germans were very slow to adopt 5.56x45 mm and had reduced power loads for their G3 rifles (again, pressure below the limits, useable in all 7.62x51 mm rifles if needed). Some of the hotter German and South African 7.62mm still being manufactured use a thinner jacket and are known to fragment similar to the M193 5.56mm ball round at the canalure. Belgian "heavy" 5.56mm gave rise to the current round (M855, 62 grain) now favored, an even heavier round is limited to special forces (Mk.262, 77 grain).
Not all NATO countries have the same rate of twist in their rifles and old rifles are sometimes fielded by reserve units, which can result in sub-optimal performance if surplus lots of ammo from one country find their way into the rifles of another.
As for tumbling, all long tapered rifle rounds will tumble in soft tissue, the amount of energy and the construction of the bullet determines the degree of instability and the point at which the bullet may break up, yaws and tear a permanent wound channel as it passes through. On impact, a high energy, long, low caliber bullet with a long, thin skinned, soft lead core bullet can bend in half, fragment into many pieces and yaw causing the nearly mythical maximum wounding potential. Faster, lighter bullets will tend to break up more easily, while more heavily built bullets will stay in one piece and continue to penetrate along reasonably straight paths, even as the bullet tumbles. Very fragile bullets begin to fragment within a few inches of penetration, while more solidly built bullets may take as much as 10 inches to do so. Temporary cavities aren't what do the real damage, it's the permanent cavities that cause the majority of tissue destruction.
-E
