The .280 AI is a SAAMI cartridge (submitted by Nosler a couple of years ago) and the pressure limit is either 64,000 or 65,000 psi, I can't recall right now.
The SAAMI limit for the 7mm Remington Magnum is 61,000. This is because the 7mm RM tends to show wider pressure variations with any given load than many other cartridges. For instance, in a typical .30-06 or .300 Winchester Magnum load the range of pressures in a 10-shot string might be 5000 psi. But a 7mm RM often shows a 10,000 psi variation between individual shots in 10-shot string.
SAAMI maximums are not just based on an average, but individual shots. They set the average at a place where any individual round won't be over a certain level--the reason the average SAAMI pressure limit for the 7 RM is only 61,000.
