I looked at the SAAMI website (
https://saami.org/wp-content/uploads/2018/01/Z299-3_ANSI-SAAMI_CFPandR.pdf) and found the following Maximum Average Pressure (MAP) values for 9MM on page 17:
9mm Luger (standard pressure): 35,000 PSI
9mm Luger +P: 38,500 PSI
Note: SAAMI does not have a standard for +P+ and does not list 9mm NATO either.
I looked at STANAG 4090 which is NATO's Standardization Agreement for 9MM NATO cartridge (
http://gigconceptsinc.com/files/STANAG4090-cartridge_9x19.pdf) and see that on page C-1 it states no individual pressure shall exceed 265 MPa (which translates to 38,435 PSI). Now, this document is dated April of 1982, but I don't suppose much has changed.
If you look at a box of Winchester "White Box" 124 gr. 9mm NATO ammunition you see this label:
It states that these cartridges are loaded to 10% higher than industry standard pressure for 9mm Luger.
Since the SAAMI pressure standard for 9mm Luger is 35,000 PSI, 10% of that is 3,500 PSI – add the two together for 38,500 PSI for the Winchester 9mm NATO round which puts it squarely on the SAAMI specification for 9mm +P as well as the maximum chamber pressure allowed for 9mm NATO out of the STANAG.
I am no expert in this – but based on the available information I am led to the conclusion that the Winchester 9MM NATO load sold at Wal-Mart and other places is operating at pressures recognized by SAAMI as 9mm +P territory.
My takeaway is this: don't treat this load like you would normal Winchester White Box 115 gr. 9mm Luger or any other standard pressure Luger load for that matter. Using the NATO load in large quantities will accelerate wear in a pistol rated for +P, just like +P does. If you are using large quantities of it in a pistol not rated for +P you may get much more than just "accelerated wear" – I am thinking more along the lines of damage over time.