45 ACP

These cartridges have the same external dimensions as the standard-pressure cartridges and will chamber and fire in all firearms designed for the standard-pressure loadings. The inner dimensions of the +P cartridge are different from the standard-pressure cartridge dimensions and thus allow for higher pressures to be safely achieved in the +P cartridge. If +P loadings are used in firearms not specifically designed for them, they may cause damage to the weapon and injuries to the operator.