I have several AR-15's in 5.56 and I am looking to build a .300 AAC Blackout soon. I am just wondering when an adjustable gas block would be required? Is it only required for when you are considering shooting with a suppressor or for sub-sonic rounds? Can any one add input /clarify? I was looking to build a pistol .300 AAC with a 9 or so inch barrel then maybe also a full 16 inch carbine build. I might shoot subsonic ammo, but I do not plan on suppressing either at this point. Would an adjustable gas block serve any purpose for either of these two builds/configurations? When would you need one if the two configurations above were 5.56?