AR308 New Frontier Armory DPMS Gas Tube Length To Short! - 13

I discovered that the RifleSpeed straight rifle length gas tube I purchased is AR-15 length at 15.250" or just slightly shorter. That's all they sell for rifle length. The correct gas tube length for "my" DPMS AR308 is Armalite Spec at 15.400". Although after measurements I believe that 15.500" would also work. I have contacted White Oak Armament for a custom 15.400" as no one sells the straight version at this dimension that I could determine. I'm convinced that this may not be the entire issue but a contributing factor to the surplus NATO that I have not holding the BCG open after the last round.