Re: A question about low-powered .308 rounds...
I do not understand why you will not realize that the two rounds are the same. Pressures stated in CUP (copper units of pressure) are NOT the same measurement as PSI (pounds per square inch). They are two different measurement systems and can be equal to each other although the numbers are different. CUP measurements WILL ALWAYS be a lower number than PSI but could equal each other!!!!
In your numbers above between velocities, the only major different are the components used to assemble the two rounds by two different manufacturers. The 107 feet per second difference in velocity is MEANINGLESS as you can have that much variation from shot to shot in ANY gun using the same lot of ammo.
The difference between the two energy figures you show is caused due to the fact that one round has a slightly lower muzzle velocity than the other. Muzzle velocity and retained velocity are part of the equation to figure out muzzle energy and retained energy!!!! If one has a lower muzzle velocity and hence lower retained velocity, it's muzzle energy and it's retained energy HAS to be lower mathematically!! The only difference in the two rounds is that the brass thickness of military rounds is usually thicker thus raising pressures if you reload. However, they are BOTH loaded to SAAMI specs which keeps them the same!!!
Do yourself a favor and take one piece of each brass (military and commercial), fill them with water to the top of the neck and then weigh them. The commercial brass will hold more water and thus weigh more than the military brass filled with water because the military brass is THICKER!
Again, the military brass and the commercial brass are both loaded to the same pressures, but are measured differently. CUP does not equal PSI nor can they be equated. The measurements systems are different, but the resulting pressures are equal!!!!
I hope this finally explains what you are looking for.