Quote Originally Posted by Kenhwind View Post
Of course the factory loads by volume, but in order to achieve the desired volume the powder would have had to have been weighed at one time, or they would not know what the volume would be. Once the reloader sets his powder measure he too is loading by volume because the powder charges do not weight the same, and I've chronographed enough rounds to believe the same is true for factory loads.
This is incorrect, and what trips most people up about volume.
They weigh it for a VMD calculation, which is a reference point only and not a goal of the load. Volume is measured in CC's, mL's or another volume measurement. They pressure test each lot, take a VMD calculation and load. Extruded powder has a very tight BR to BD control. A consistent case fill is what they are after. If the BD changes there is a corresponding inverse relationship with the BR. So if there is more nitro(power) then the burn rate slows down; with the inverse also being true. In this way the powder will always produce a consistent pressure. The weight may or may not change much, but the case fill is always the same.