the 223 is more than a serviceable SD cartridge when used in the right format.
In my opinion along with lots examples.
The 223/5.56 mm round performs best and is very destructive.
When using a 55gr projectile moving above 3000 fps.
Thats why the M16 A1 pushing a 55gr fmj through a 20 inch 1-12 twist barrel
in the 3000+ feet range was so successful.
It was not until they started making the platform more user/ Mission adaptable package that the performance started to slip.
In my opinion the 223 in a carbine is not an effective combination.
Thats why you see the heavier and heavier bullets trying to get some performance out of the M4's
With the carbine length AR's your just not pushing the round fast enough.
Instead of the devastating tumbling action of the 55gr rifle load. Your getting 22 cal sized holes.
I have seen video of a 55gr fmj (ball) load shot from a 20 inch 1-12 rifle penetrate a steel plate.
At the same distance a green tip 62gr steel penetration load shot from a carbine could not penetrate.
So Mr Stoner actually did have the right formula the 1st time. It was not until we started messing with it that the performance suffered.
That is why I went to the 30 cal 300 Black out to cover my Carbine needs and built a 20 inch 1-12 .223 rifle for my 223 work.
With the 223/ 5.56 speed is king.
Thats my story and I built to stick too it.