When you have a doubt the best is to go straight to the source.
We had a question about the ammunition and went to talk to Fiocchi technicians, in Italy. Arriving to Lecco the fog keep off to see the mountains and the lake. It was a pity because it seems to be a nice landscape (the picture was token from the car, when I went out).
I went to ask if they manufacture as standard overpressure ammunition to make the pressure test at the approval of the weapon.
The answer was clear: "It's forbidden to manufacture ammunition with a greater pressure than established by the CIP" meaning that it's a statistical measure and it could have some uncertainty due to the measurement error. They said also the use to work as much as 10% below that pressure.
In other words, the called "+P" ammunition may have a higher pressure and could increase the projectile speed but NEVER will exceed the maximum values of the CIP for that ammunition.
If you want to get test ammunition must be hand loaded and check the pressure for that charge.
I had heard of some tests with ammunition at 60 ° C. They told that ammunition is extremely dangerous to manage under those conditions (of course) and temperature increases the pressure but is not linear.