jmcusa posted:
“...The M-16 is a high velocity weapon. ... a high velocity round hits hard, however, ... an enemy and he might not go down right away. The M-1, ... low velocity rifle ... stopping power and penetration of the M-1 is legendary....”
dglang posted:
“...The U.S. has machine guns utilizing the NATO 7.62 rounds because of their greater range, accuracy and stopping power.
Unfortunately, the military favored the M16 for it’s lighter weight of both the rifle and the ammo with the lighter and smaller ammo allowing the soldier to carry more of it. On the other hand, the smaller and lighter ammo just doesn’t have the stopping power of the larger and heavier 7.62 round. ...”
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“Stopping power” is a concept worshipped by most of US civil gun culture, but it has no formal definition and has resisted all attempts at quantification.
5.56x45 NATO in US M193 loading (original M16): 55 gr bullet, 3250 ft/sec
US Rifle Cartridge, cal 30, M1906 (30-06): original loading 150 gr bullet, 2700 ft/sec. 30M1 loading: 172 gr bullet, circa 2550 ft/sec; 30M2 loading: 153 gr bullet, 2750 ft/sec
7.62mm NATO, US M80 loading: 147 gr bullet, 2750 ft/sec.
So muzzle velocity varies some 20 percent, highest to lowest.
All three are “high velocity” in that they leave the barrel at multiple times the speed of sound (nominally 1140 ft/sec at sea level, varies with temperature).
Peter G Kokalis, longtime gun writer and one of the few military shooters who has attempted to discuss small arms ordnance in terms the average civilian gun owner can grasp, claimed circa 1990 that the 5.56 was more effective inside 100m than either 30 cal round (we can likely take 30-06 and 7.62 NATO as identical, in issue ammo); effective against unarmored human targets, that is. This was, he stated, because the M193 bullet would fragment on impact, where the 30 cal bullets would go clean through. The best predictor of incapacitation of an enemy hit by a bullet is energy transfer to the target; the 5.56 thus gave up most of its 1290 ft-pounds on fragmenting, while the 30 cal bullet (roughly three times as massive) gave up a small fraction before exiting the target to dump whatever remained of over 2300 ft-pounds of energy on the background.
Please note: “best” predictor does not mean “perfect”.
Tradeoffs are unavoidable.
The 5.56mm round has a far shorter effective range: 450m compared to 600m for the 7.62mm bullets (1100m for high-accuracy and tripod-mounted machine gun applications). No terminal-effects research has come to light, to confirm (or deny) the “harder hitting” theory. Possibly because humans vary so much in size, organ and bone mass and positioning, metabolic state, state of excitement, and the impossibility of collecting repeatable data.
Each 5.56mm round weighs only half what a 7.62mm round weighs; hence, any given soldier could carry twice as much ammunition while humping the same weight. This dovetailed with the firepower theories being promulgated in the 1950s, in US Army training and doctrinal development circles. Namely, aimed fire means little, therefore put as many rounds into your target’s general vicinity as possible. With this constraint, a bullet that was “good enough” on hitting was the key. All in all, it was deemed better to carry more shots than to risk running dry. Most fired rounds missed anyway.
US machine guns chambered 7.62mm NATO because that was what was being issued at the time of their development. Considerations of shot-for-shot effectiveness and range did not drive the situation.
Various agencies did undertake various projects from about 1960 onward, to improve the effective range and terminal effectiveness of the 5.56mm bullet. Many were built with use in machine guns in mind. The variety of possible “improvements” was pretty broad, from higher-velocity needle-like projectiles, to bullets of larger diameter loaded into the 5.56x45mm cartridge case, to cartridges of different calibers and sizes (23 cal, 243 cal, 257 cal, 264 cal, 27 and 28 cal to name just a few). Telescoped ammunition (bullet inside case), flechette rounds, and multi-bullet rounds were tried out, as dglang pointed out.
No increase was discovered in effectiveness, at least not to a level that would justify the expenditure of adopting a different rifle and cartridge, then rearming the military.
The US M249 Squad Automatic Weapon (developed from FN’s Minimi) was developed on purpose, chambering 5.56mm NATO, to give US foot troops more of a sustained fire capability without forcing soldiers to carry mutually incompatible ammunition. Primary feed device is a disintegrating link belt, but M16 box magazines can be used instead, enhancing interoperability inside the fire team.