I have seen terms like +P+ and +P for ammo, what do these things mean. Is there any web sites out there that have definitions to these kind of terms? Thanks in advance.

+P means higher pressure levels/limits than the standard ammo. +P+ is the same as +P (NOT even higher pressure). With the higher pressure comes a (slight) increase in velocity.

257Roberts 45000cup/54000psi
257Robt's +P 50000cup/58000psi
38spl 17000cup/17000psi
38spl +P 20000cup/18500psi
45ACP 21000psi
45ACP +P 23000psi

"Plus P" and "Plus P Plus" ammunition is simply ammunition loaded to higher than normal SAAMI (Sportings Arms & Ammunition Makers Institute) pressure specifications.

"Plus P-ing" was first done with law enforcement pistol ammunition in an effort to wring the last bit of power out of a cartridge. For most rounds the gain in performance is minimal and leads to increased wear and tear on the firearm.

+P pressures are generally around 7% to 10% higher than standard SAAMI pressure limits.

The +P+ ammunition is loaded to even higher pressure levels than +P.

There are no SAAMI specifications for +P+ loads, but by general industry agreement they are about 15 percent greater than +P.

Standard 9mm 115 gr. bullet goes 1150 FPS.

+P 9mm does 1250 with a 115 grain bullet.

+P+ 9mm does 1350 with the same bullets, which approaches 357 velocities.

9mm can be loaded to higher power levels still, like a 125 grain bullet at 1350 FPS, but the pressures would make certain people cringe.

The 9mm is an amazingly efficient cartrige. I used to hate it, but now I appreciate the flexibility and ease of use.

Thank you very much for clarifying these terms. Now I am a little more prepared for the things I read online.