I am running SB3's on both my 308 pistols with the Armalite 308 carbine buffer tubes ,springs,and buffer. If it is a virgin lower and you build it as a pistol then it doesn't matter on the barrel length. Some states DO have overall lengths to be considered a pistol. I also have the tailhook 2 on my 300 blackout pistol. I do like it I just don't want to mess with buffers and springs to move it to one of the 308 pistols.