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Old September 19, 2011, 01:46 PM   #7
Unclenick
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Join Date: March 4, 2005
Location: Ohio
Posts: 10,247
Another way to look at it is if you set COL for a pressure minimum, you can add more powder. That raises remaining pressure at the muzzle, even if the peak is the same, so average pressure is raised, increasing velocity. You see the same thing with adding powder to get back to a given peak pressure when using bullets with dry lube coatings, like moly. More velocity at equal peak pressure.

The problem is, how do you find the minimum pressure COL? The graph I posted was for a round nose bullet (only numerical data I had) in a 1903 Springfield rifle, but a spire point can find the pressure minimum a shorter distance off the lands. RSI's information on their Pressure Trace instrument has a pressure plot of a 6 PPC round's pressure dropping 20% just from coming back 0.030" off the lands. Unfortunately, you need instrumentation to know where it will happen with your particular bullet and chamber and whether that's a practical objective for you or not?
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