Should also add that the standard allowable SAAMI variation in headspace for most rifle cartridges is plus or minus .007"--exactly half of the difference between the "Ackley" .290 AI and the "Nosler .280 AI." Again, this is typical rifle-loony obsessive minutiae.

“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.”
John Steinbeck