M193 5.56 pressure is driven by a need to meet a velocity spec, 3,200 FPS. You do realize that the AR15 round came first, Eugene Stoner developed it from the 222 Remington and called it the 222 Special then Remington released it as the .223. So as far as when around late 50's early 60's.
“The Trump Doctrine is ‘We’re America, Bitch.’ That’s the Trump Doctrine.”
"He is free to evade reality, he is free to unfocus his mind and stumble blindly down any road he pleases, but not free to avoid the abyss he refuses to see."
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