The Tech did say because of the smaller case volume, less powder should create the same velocities as the larger case with higher powder charges. interesting stuff!
If you are looking to get rid of those XPBs I may know a buyer!
Case volume with the loaded bullet plays a huge roll in velocities. If you ignite the same amount of powder in a smaller volume the pressure gets higher and pushes the bullet faster. If you ever do some extrapolating between loads and different bullets, you need to pay attention to where the back of the bullet is between the different loads and what the available volume is inside the case. As Barnes said, different case brands play a roll too. Internal ballistics in a gun is a fascinating subject with lots of nuances.
If you do want to sell the XPB's i would take a few but am not planning on shooting a lot of them.
