Note: 300 Blackout has a short effective range, the rifle in the photo had a very short barrel. That type of rifle will have an effective range of 100-150 yards. It is NOT a sniper rifle.
Idiots write the News articles. Clueless.
I custom built my 300BLK SBR with a 10.5" barrel. The powder is burned by 9.5". Nothing to gain with more barrel. The shorter barrel allows for adding a suppressor yielding a nicely balanced SBR. Purpose built for hog hunting. Getting the gas port placement is important. A pistol port placement works well. Tuning for supersonic/subsonic is yet another chore.