For you folks that are trying to wrap your head around the ramifications of this seating depth thing, you might want to do a little research on Boyle's Law of Gases. I also strongly recommend that you seek out load manuals from the manufacturer of the bullet you are working up a load for. You also would be well advised to compare that data with that of the powder manufacturers. I also strongly recommend getting a chrono to verify the results in your individual firearm. For you people that shoot jacketed bullets from manufacturers that also sell loaded ammo with your bullet of choice.........buy a box of factory ammo and examine it for COL. It never hurts to go back and re-read your load manuals to make sure you are not developing any BAD HABITS!