Yep, sure 'nuff, John. I always attempt to verify info that I can't readily find a source for. But you are on your toes...................LOL.
And yes, I do realize that 20" may be smaller than 18" RG because of the added dwell time. But I also realize that more of the powder has burned in the longer barrel, which lowers pressure, requiring a bigger gas port. More that just one variable.
But, nonetheless, assuming the OP has no other issues that he hasn't found or told us about, he is simply short of gas with that ammo, at whatever temp he's shooting with a .093" port.
And also, as I said earlier, it's easier to deal with a little over-gassing.............compared to being under-gassed, especially if he wants to shoot lower powered ammo.
YMMV
MM
