+p+ does not have a standard. The designation literally means that the cartridges are loaded beyond SAAMI spec. How much beyond, is up to the maker.
Still happily answering to the call-sign Peetza.
You do not HAVE a soul. You ARE a soul. You HAVE a body.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.