Naval Surface Warface Center-Crane conducted tests to see if Mid-length gas system is better.
Answer: Yes
Muzzle velocity is more or less the same, but velocity at 100 yards show different story.
http://soldiersystems.net/2018/05/14/nswc-crane-carbine-mid-length-gas-system-testing-shows-increased-performance/
From: Soldier Systems Daily
