Field Guide · Compatibility
+P is a real, SAAMI-standardized overpressure designation — not a marketing label. It means the cartridge is loaded above the standard maximum pressure for that caliber, at a specific pressure level SAAMI has defined and published.
SAAMI (Sporting Arms and Ammunition Manufacturers' Institute) is the U.S. standards body that defines pressure limits, chamber dimensions, and safety specifications for commercial ammunition. When SAAMI establishes a +P pressure level, it becomes a real spec — manufacturers who label ammunition "+P" are certifying it was loaded to meet that defined standard.
Not every caliber has a SAAMI-defined +P level. SAAMI defines +P for handgun cartridges where there is established industry practice of loading higher-pressure defensive ammunition and where it's practical to set a standardized upper limit. Rifle cartridges generally do not use the +P designation — the equivalent concept is handled by distinct chambering designations (e.g., .308 Winchester vs. .300 Win Mag).
| Cartridge | Standard Max (SAAMI) | +P Max (SAAMI) | Increase |
|---|---|---|---|
| 9mm Luger | 35,000 psi | 38,500 psi | +10% |
| .38 Special | 17,000 psi | 20,000 psi | +18% |
| .38 Super Auto | 33,000 psi | 36,500 psi | +11% |
| .45 ACP | 21,000 psi | 23,000 psi | +10% |
| .40 S&W | 35,000 psi | No SAAMI +P standard | N/A |
| .357 SIG | 40,000 psi | No SAAMI +P standard | N/A |
The +P+ designation appears on some law enforcement and specialty ammunition. Unlike +P, there is no SAAMI-defined pressure level for +P+. Each manufacturer who uses the +P+ designation sets their own pressure ceiling. The designation is not standardized and not regulated by SAAMI.
Some law enforcement agencies specify +P+ loads for their issued firearms. In those cases, the firearm selection was made with +P+ compatibility in mind. For civilian use with commercially purchased pistols, verify with the manufacturer before using +P+ ammunition.
Terminal ballistic performance in defensive handgun ammunition depends on bullet velocity at the moment of impact. Hollow-point bullets are designed to expand to a specific diameter at a minimum velocity threshold — below that threshold, the bullet may not expand reliably, which significantly reduces its terminal effectiveness.
From a compact or subcompact barrel (3 to 3.5 inches), muzzle velocity is lower than from a full-size barrel (4 to 5 inches). +P ammunition's additional pressure recovers some of that velocity loss, which is why +P loads are disproportionately popular for compact carry pistols with shorter barrels.
The tradeoff is wear. Higher pressure cycles the action harder, compresses the recoil spring more fully, and increases the force transmitted to the frame. Manufacturers account for this by rating certain firearms for +P and specifying reduced practice volumes with +P loads.
The velocity increase from standard to +P is real but not dramatic. In a 4-inch barrel, a standard-pressure 124-grain 9mm load runs approximately 1,100 to 1,150 fps. A +P load of the same bullet weight typically runs 1,200 to 1,250 fps — a gain of roughly 50 to 100 fps.
Whether that gain matters depends on the specific bullet and its expansion velocity threshold. Many modern hollow-point designs expand reliably at standard-pressure velocities from full-size barrels. For subcompact barrels, the +P velocity becomes more relevant to reliable expansion in compact carry guns.
+P is a SAAMI-standardized overpressure designation with a defined pressure ceiling. It is relevant and real — check whether your specific firearm is rated for it before regular use. +P+ is not a SAAMI standard and should only be used with explicit manufacturer approval.