What Does +P Mean? +P and +P+ Ammo Explained
The Short Answer
+P means higher pressure than standard. For 9mm: standard max pressure is 35,000 PSI; +P is 38,500 PSI (a 10% increase). The velocity gain is typically 50–100 fps, translating to roughly 10–15% more muzzle energy. +P+ has no SAAMI specification — each manufacturer sets its own limits, with pressures estimated around ~42,000 PSI.
The SAAMI Pressure Specs
| Rating | 9mm Max Pressure | Increase Over Standard | SAAMI Standard? |
|---|---|---|---|
| Standard | 35,000 PSI | — | Yes |
| +P | 38,500 PSI | +10% | Yes (SAAMI Z299.3) |
| +P+ | ~42,000 PSI (estimated) | +20% (estimated) | No — no standard exists |
| Proof load | 45,700 PSI | +30.6% | Yes (testing only) |
These are SAAMI Z299.3 piezoelectric transducer measurements. The proof load is used only for factory testing barrels and is never intended for regular shooting.
What +P Actually Gets You
A typical +P velocity gain is 50–100 fps over the standard-pressure version of the same load. For example, Federal HST 124gr standard runs approximately 1,116 fps from a 4" barrel, while the 124gr +P version runs approximately 1,150 fps. That translates to roughly 10–15% more muzzle energy.
Is that meaningful? In gel testing, the +P version of most loads penetrates 0.5–1.5 inches deeper and expands to a similar diameter. The difference is real but modest. Where +P matters most is in short-barreled guns (3–3.5" barrels) where standard-pressure loads may be borderline for reliable JHP expansion. The extra velocity from +P can push a load over the expansion threshold.
Can Your Gun Handle +P?
Most modern firearms from major manufacturers are rated for +P. Glock, SIG, Smith & Wesson, Springfield, CZ, and others confirm +P compatibility in their manuals. The general guidelines:
Check your manual. If it says +P is approved, you're good. If it says nothing about +P, contact the manufacturer. If it says +P is not recommended, don't use it.
Recoil spring replacement: +P accelerates wear on recoil springs. Most manufacturers recommend replacing the recoil spring every 2,000 rounds of +P versus the normal 3,000–5,000 round interval. This is a $10–$20 part and five minutes of work.
Older or budget guns: Vintage firearms (pre-1990s), lightweight aluminum-frame revolvers not specifically rated for +P, and some budget pistols should not shoot +P unless the manufacturer explicitly approves it.
The +P+ Problem
Most gun manufacturers do not officially rate their firearms for +P+. Glock tech support has confirmed their pistols will handle +P+ factory ammo, but this is verbal guidance, not a published warranty statement. Running +P+ voids most warranties and accelerates parts wear beyond what +P does.
For most shooters, +P is the ceiling. The marginal velocity gain from +P+ over +P is small (typically 25–50 fps), the recoil increase is significant, and the lack of standardization means you're trusting each manufacturer's internal pressure testing with no SAAMI safety net.
The Bottom Line
+P is a useful option for carry ammo in short-barreled guns where the extra velocity ensures reliable JHP expansion. For full-size guns with 4"+ barrels, standard-pressure loads perform excellently and wear your gun less. +P+ is unnecessary for civilians — the marginal ballistic improvement doesn't justify the increased wear and lack of standardization.
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