I recently purchased a 300 Blackout carbine. Right out of the box I started having trouble with subsonic rounds not reliably ejecting the casing and not picking up the following round. I have learned that the 300 BLK pistol barrel "gas port" is around 7" fro the breach and the carbine is around 11". This difference doesn't allow the subsonic to create enough back pressure to fully recharge the bolt. I'm told that a suppressor might create enough back pressure to shoot subsonics? Does anyone out there agree with this? Next question: I can buy a carbine barrel with a pistol gas port. Does this created a problem with shooting supersonic rounds??? The twist is 1:7 on a carbine barrel and 1:8 on the barrel drilled for the pistol gas port. Is that a problem? I appreciate any knowledge on this!