Originally Posted by
MostlyLeverGuns
The point of more powder and less speed is valid in some cases. I have found that as a powder charge is compressed, velocity may slow down until enough powder is added to make up for the reduced powder ignition due to powder compression. I ran into this in several rifles, .243, .308, and even the .45-70. It always occurred when a powder charge went from 98-99% case fill to moderately compressed, velocity could be regained by going to 'hotter' magnum primer OR adding yet another grain or two of powder, but there was a spot where another grain or two slowed things down, my best guess is the compression reduced ignition and or modified burn rate.