I think "nato" in this case refers to nato type ammo. As in full metal jacket and within nato specs. When I was in the AF, in the 80s, the military switched to the Beretta 9mm so we could be within nato spec. This was supposedly because we would be able to all fire the same handgun caliber if several nato countries were deployed together. If the commercial 9mm you got was hotter than Sami spec there would be dire warnings about shooting this stuff on the box. If it was +p it would say so on the headstamp and the box. As others have said, there shouldn't be any problem shooting major brand 9mm ammo in any M&P.

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Tom
"Panem et Circenses"