I finally got around to measuring muzzle velocity on the AAC 5.56, 55gr Vmax ammo I bought in Jan 2023. Fired from a 16" barrel with .223 Wylde chamber, 1/8 twist.
The 5 shot average was 3031 fps. I believe with a 20" or 22" barrel the velocity would be the same as on the box, 3175 fps. Standard deviation was 14 
and the extreme spread was 37 fps.
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This 16" has the carbine length gas system. I use an H2 buffer, since it appears over gassed, IMO. Your chart shows the same velocity for any 16" barrel; no matter what gas tube length.
The location of the gas port has very little to do with the velocity of ammunition. The pressure drops by more than 75 % at the port to 13000 psi in MIl-Spec ammo. The reduction in barrel length is much more detrimental to muzzle velocity.
As to the overgassing marketing hooey of buffers and springs: Winter conditions (- 65 degrees F) can result in port pressure drops of 2000 psi for a rifle length system. AR rifles are “gassed” to operate reliably in those conditions, so they will be “overgassed” in the summer. Older ammo will degrade and 223 Remingnton will produce lower peak pressures in NATO or Wilde chamber by as much as 7,000 psi. Heavy buffer rifles may become unreliable is “gassed” for NATO loads.
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FL 35 or so and up in elevation any time of the year.
Was trying to generate conversation on the thread mainly. I made no claims, merely asked a question.
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