I built a Stag 10 in 6.5cm , was short stroking 98% of the time even with the adjustable gas block opened all the way. Tried a new gas block , tried a different BCG all kinds of ammo , no luck . i have a 20'' Faxon Big Gunner barrel, its a DPMS LR308 pattern barrel with a rifle length gas system , also using a Faxon BCG .
I used a rifle length AR15 gas tube but then i noticed the gas tube was not protruding into the upper as much as my AR15 rifles , seemed too short in there .. After some research i found that the Armalite gas tubes are just a bit longer , so i ordered a rifle length Armalite tube installed it and she runs like a champ!! I thought DPMS LR308 pattern barrels and uppers use AR15 tube lengths? or is this just a issue with the Faxon barrel ? Hope this helps someone else .. If your gas tube looks like the one in the top pic get a Armalite tube!
AR15 rifle length tube
Armalite rifle length tube