Originally Posted by bastover
If you say so.
Well, SAAMI says so. I just echoed what they state. That aside, all the atmospheric conditions effect how the bullet flies down range.
Stop and think about how there's any way the geographic location, barometer reading and humidity could effect how powder burns inside a virtual air-tight container. Then try to find any reference from any source that states there is an effect. Powder temperature will definitely make a difference, but smart people make comparisons with powder at the same temperatures.
The following SAAMI document lists the conditions for testing ammunition for pressure and velocity:
Page 94 and 95 lists the conditions for testing ammo. The only environmental condition is that ambient temperature be from 60 to 80 degrees F. Nothing about geographical, barometric or humidity requirements.
That whole document's got information that usually surprises folks.