Hi Roger. A cartridge that is marked +P (+ Pressure) is slightly more powerful than a standard pressure cartridge of the same caliber. This will result in higher velocities and energies. The shooter will want to make sure that their firearm is rated for +P ammo before firing. Generally speaking, a revolver chambered for .357 Magnum can safely fire .38+p ammo as can any revolver marked "38 Special +P" on the barrel or frame. Always check with your firearm's manufacturer to find out if you are unsure.