>5.56 was adopted from .223, a common small game cartridge at the time.
No, .223 wasn't a common cartridge, it was designed from the ground up to be the cartridge for the AR-15. .223's parent case was .222 Remington, which was a target shooting round that also saw some use as a varmint round. However, saying .223 is just "adapted" .222 is misleading at best. .223 uses a different bullet, a longer case, a different shoulder, and much higher pressures; the two are different cartridges with different intended purposes. Likely the only reason the author of that pic took note of this at all is so he could >imply that 5.56x45 was a no-good poodleshooter of a varmint round, by pointing out that .223's predecessor was a varmint round.
>it was found that hte common ~40 grain .223 was too light
No, .223 was intended to use a 55 grain projectile from the beginning of the design process. .222 Remington's most common loading was 40 grain, yes, but .222 is not .223. As stated above, .222 is just the parent case but a fundamentally different cartridge. Again, the original poster is bringing this up to >imply that .223 was modified ad-hoc during the design process.
>However the 55 grain was found to be too affected by foliage...so the bullet was lengthened to make it more than 60 grain
No, the 62 grain M855 was adopted primarily because NATO was being retarded in the 70s. NATO standards at the time called for the service cartridge to be able to penetrate steel helmets at 600 yards, so they adopted a cartridge with a mild steel core that was able to meet these requirements. The change had nothing to do with any inherent flaw within the 55 grain M193. In fact the M193 performs better against soft targets, and within shorter ranges (remember that 600 yards is well beyond the effective range of the AR-15) actually has better penetration performance against steel.
>the twist rate was increased to 1:7, which more than doubled the ball ammo grouping.
This is just retarded. As long as the twist rate is fast enough to stabilize the bullet and prevent keyholing, and isn't so fast that the bullets explode midflight (in practical terms this upper limit is never reached unless you're intentionally mismatching bullet length and twist rate to see if you can make bullets explode), twist rate has no significant effect on accuracy. If you're a precision shooter, maybe
you'll start to notice that your shots are veering off to one side or another. A faster twist rate means your bullets spin faster, which would make the bullet yaw a bit in the direction of rotation. However, this effect is minuscule. Only precision riflemen making 800 yard shots from a bench rest will even notice it occurring. It certainly wouldn't "more than double the grouping." The M855 loading isn't particularly accurate, but this is because the bullet has a steel core set into the lead surrounding it. This introduced another potential inconsistency in ammunition production, because the steel cores weren't perfectly inset from one bullet to the next. And the only reason the steel core M855 was adopted was due to NATO autism, as said before.
>however soldiers complained about its length while in a vehicle
This may well be true but it had nothing to do with the design process behind the M4. The M4 was designed for SOCOM, who wanted an extremely compact rifle so they could operate operationally. Original poster is half-right in that the compactness of the rifle is what lead the Army to adopting it as the service rifle afterwards, and adopting a specialized carbine as your general-issue service rifle is retarded.
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