I noticed you don't put the port size on all your barrels on your website.  I recently purchased  a 12" 6.5 Grendel barrel. I've been having a problem with under gas/short stroking.
Can you tell me what your port size is on these? I took it back apart and it looks to be around .073?
I'm shooting it unsuppressed and plan on shooting it that way. CAR standard buffer and spring. Gas port shows that I had the gas block installed correctly over the port and no leakage.

I have had the exact same problem. I even contemplated enlarging the port.