Anybody know what's the difference in +P and +P+ ammo?

+P+ is loaded to the maximum SAAMI specs I think. Very hot.

The last time I looked at the SAAMI website, they do not list a specification for +p+. AFAIK, that designation not an "official" one, but is commonly used for overpressure rounds that are even higher than regular +p. I believe that the 9mm NATO round can be considered a +p+ round.

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I believe that the 9mm NATO round can be considered a +p+ round.

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It's hard to compare the two: you're comparing apples and oranges.
My understanding is that SAAMI specs look at the chamber pressure at roughly the case midpoint. NATO, or European specs, measure pressures at the case mouth, which are inherently higher than at the case midpoint. If you measure the same round using the two different forms of measurement, NATO measurements will always appear higher.

That's the extent of my knowledge - they're not comparable. Maybe someone who stayed in a Holiday Inn Express can enlighten us further.

Both are loaded above SAAMI specs. Once a round exceeds the max pressure then it has to have a +p designation.

In actuality you could have a +p and a +p+ loaded to to same pressure since once it exceeds SAMMI then there no way to accurately notate it

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Both are loaded above SAAMI specs. Once a round exceeds the max pressure then it has to have a +p designation.

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That is somewhat incorrect. +p is an official SAAMI designation, with the specs to go along with it. Therefore, a +p load isn't loaded above SAAMI specs -- it is SAAMI specs.

The +p+ designation is not listed on the SAAMI list of officialy recognized specifications. It is however commonly used to denote an overpressure round above regular +p. The specs for normal and +p 9mm can be found at the link below.

http://www.saami.org/specifications_and_information/publications/download/205.pdf

Sorry, I guess I got confused on the above pressure deal