I think after 6 pages of rehash and conjecture, it's time to use a picture. This is an image from a Quickload program which illustrates what 'rlspahn' is trying to get across as usable information. All of this is very simple. The powder is ignited from the back of the cartridge which builds pressure, pushing both the bullet and the remaining powder forward though the barrel. At 16.16" (in this example) the powder charge has been fully consumed but the pressure still remains albeit, it is reducing until it reaches the muzzle at 22" still pushing at 18,250 PSI. None of this is hard to understand but it can be a little tedious to try to picture what is actually taking place. The image above illustrates what is happening in the barrel from ignition to just as the bullet leaves the muzzle. The cartridge is the 6.5 RSAUM loaded with the Berger 130 gr. VLD hunter which, at this velocity will generate 1,000 ft/lbs of energy at 800 yards. All of this information is located at the bottom of the illustration in red typeface. The same data can be generated with the 6.5 PRC within a FPS. Enjoy the process!