Originally posted by Sundo:
I've seen charts that say the dwell time increases from 0.018 to 0.023 seconds between a 16 in and 18 in barrel with a midlength gas system, using 55 gr ammo.
For starters, your numbers are WAY off. It takes a 55 grain bullet less than 1 millisecond, that’s 0.001 seconds, to travel the entire length of an 18” barrel. It takes less than 0.9 milliseconds, 0.0009 seconds, for that 55 grain bullet to travel the entire length of a 16” barrel. The difference between the dwell times of a 16” barrel and an 18” barrel that both have a mid-length gas system will be approximately 0.06 milliseconds; that’s 0.00006 seconds.
55 grain bullet from 18” barrel

55 grain bullet from 16” barrel

Originally posted by Sundo:
My theoretical intuition tells me that the longer dwell time of the 18 in barrel should result in less accuracy than the shorter dwell time of the 16 in barrel, since all else is equal.
A. I’ve never seen a single study showing a causal relationship between an increase in the amount of time that it takes the bullet to travel from the gas port to the muzzle and a decrease in accuracy in an AR-15.
B. “All else” is not equal.
.....
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