Think of your Tank as the Engine and the Barrel as the Transmission, cut the barrel and you cut a gear
Here is what I have found with any of the Texan Carbines Vs Long Rifle
When you are shooting lighter bullets in the caliber range you will not see any real difference in Velocity that being said once you cross the preverbal line from light to heavy lead in the Caliber you are shooting you will see a dramatic drop in FPS and FPE
The .50 Cals has a pretty dramatic ballistic arch as it is and it takes some FPS to keep you from having to treat your gun as a mortar shooter.
Shooting from a Heli your working with gravity and it will not be as noticeable but ground to ground is a whole different story.