I doubt a factory Stag would have gas block issues.
If you’ve got a rifle length receiver extension, use a rifle buffer and spring. You’re cheating yourself if you don’t.
24” barrels can have issues with carbine receiver extensions, buffers and springs. Different gas system than a rifle on a 20” due to 4” extra dwell time. Hard to say but I’d guess heavier might be better just nothing but guesses without seeing it. I’d start with the rifle lower, get it sorted out first with both uppers. That way you’re not chasing your tail with so many variables.
I suspect the BCG’s are your hiccup. But again, I’m just guessing from this point.
