One thing we know for sure.
5.56 can take off a bicep at close range.
And a shot to the chest appears pretty lethal.
Still want a short cased, high pressure, mag compatible with standard lower .243 for an AR though.
Ah, some real-world evidence of what some Speer/CCI reps said a while back —>
Most of the conversation is about pistols, but it comes down to human elasticity, I.e. the human body can’t cope with the force of a 55gr projectile traveling 2-3x the speed of sound.