gnoahh,
It's been proven, in many formal tests, that a shoulder angle of about 30 degrees results in the most consistent pressure (and hence velocity), especially in short-cases cartridges; 20 and 40-degree angles do not result in the same consistency.
The first shooters to make a real study of this, as I recall, were Lou Palmisano and Ferris Pindell, when they were developing the PPC rounds, but 20 and 40-degree angles do not. Which is exactly why so many "accuracy" cartridges over the decades have 30-degree shoulders, including (perhaps accidentally, perhaps not) the .219 Wasp, developed by Harvey Donaldson before WWII. Today's line-up of 30-degree shoulder, short cartridges includes not just the 6.5 Creedmoor but David Tubbs 6XC, 6.5 Grendel and the the 6.5x47 Lapua, along with others.
Now, this shoulder angle's accuracy potential may not show up at closer ranges (though I have seen it over and over again in various 6.5 Creedmoors), and it may not be relevant to those shooters who primarily consider muzzle velocity the essential attribute of any cartridge. But it's there.
Thanks, John.
