barrel length, gas system, dwell time, accuracy
Here's a question for you AR gurus:
I'm trying to choose between two ARs that are identical, except for a barrel length difference of 16 or 18 inches. The gas block is in the same location relative to the chamber end, at the midlength position. This means the length of barrel in front of the gas block is 2 inches longer on the 18 inch barrel than on the 16 inch barrel. In turn, this means the dwell time (bullet between gas block and muzzle) is correspondingly longer in the 18 inch barrel.
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. (I expect to use 77 gr ammo, so I expect the dwell time to be a bit longer.)
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. I notice that the SPR design uses an 18 in barrel with an intermediate length gas block, which puts the gas block further forward than the midlength system.
So my question to AR technical gurus, and those who have experience with the situation above: Are my concerns above valid? Is the accuracy difference measurable (and consistent) in bench rest groups with heavy match ammo? Does anyone have examples of bench rest results that show a clear difference (or clearly no difference)?
I'm trying to learn the results from expert experiences, rather than try to buy both and figure it out on my own. Thanks!