+P refers to the pressure of the loading. Read the SAAMI page for more info on what the designations mean.


As to the OP's Q: that will depend on the individual gun and the individual load. While it is difficult to figure out what's an apples-to-apples comparison, I have found there's not always much difference between the velocities delivered by very similar loadings (same bullet, same maker) of standard or +P designation.



For instance, out of my 3" SIG-Sauer P938 (Range at 5950’ > sea level, c. 73°F, c. 45% humidity), Remington's standard pressure 124-gr Golden Saber BJHP did 1056 fps/61.29 spread/23.28 deviation



and the +P variant with the same bullet did 1114/20.02/12.76. In that little, light gun, I'm carrying the standard pressure variant.

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