Understanding 9mm +P Ammunition

Understanding 9mm +P Ammunition

9mm Plus P ammo is loaded to higher pressures, but that doesn’t necessarily mean it is better than standard pressure ammunition.

Many shooters believe that 9mm ammunition with the +P label is much more lethal than ammunition without the same designation. The +P is thought to mean more power when in fact what it really means is more pressure. More pressure can translate to more power, but that does not necessarily correlate to increased lethality or stopping power, whatever you think “stopping power” might mean.

To fully understand what +P ammunition is, you must first understand how the manufacture of commercial ammunition is controlled. An organization known as SAAMI, which is the Sporting Arms and Ammunition Manufacturers’ Institute, establishes guidelines for ammunition production. These guidelines stipulate the sizes and pressures of commercial ammunition. Most major ammunition manufacturers follow SAAMI guidelines to ensure that all the ammunition they manufacture will function safely in all guns. This is what allows 9mm ammunition manufactured in 2020 to work perfectly in a 9mm handgun made in 1990, or vice versa.

How Much Faster is 9mm +P Ammo?

For the 9mm Luger cartridge, SAAMI established a maximum average chamber pressure of 35,000 psi, and ammunition companies adhere to this. After all, they don’t want their ammunition to blow up a gun. About three decades ago manufacturers began loading the 9mm to higher pressures, and SAAMI created a category for 9mm +P ammunition, with a maximum average pressure of 38,500 psi. This increase in pressure generally amounts to about a 5 percent increase in velocity. It’s important to note that some 9mm handguns are not rated for +P ammunition.

The increased pressure and velocity can increase bullet deformation and/or penetration, but rarely both. This is because the larger frontal diameter a bullet develops during deformation, the less it will penetrate. Also, some 9mm ammunition is rated as +P+, meaning it exceeds the maximum allowable pressure limit for 9mm +P ammunition that has been established SAAMI. It gets complicated because SAAMI does not have a classification for +P+ ammo. This does not mean there are no handguns that can handle +P+ ammo, most rated for +P ammunition will, but a steady diet of it is not recommended.

Can Your Handgun Handle 9mm +P Ammo?

When it comes to deciding if you should use +P 9mm ammunition in your handgun, the first step is to determine if your handgun is rated for it. This is generally discoverable by looking in the owner’s manual. The next consideration is if it is worth the increased wear on your handgun. The use of +P ammunition for practice is generally not a good idea; there’s no reason to expose your handgun to the extra stress that often. If you use +P ammo at all, it should be as carry ammo, and for the purpose of either increasing the penetration depth or the diameter of the expanded bullet, so to increase tissue destruction.

9mm +P Ammo With Short Barrels

The extra velocity generally provided with +P ammo can be a good thing with short barrel handguns. The extremely short barrels on many modern ultra-compact 9mm pistols can reduce velocity, and this can sometimes be detrimental to terminal performance. The increased impact velocity of the bullet with +P ammo can help with bullet upset. But the increase in pressure and velocity also increases recoil, sometimes by as much as 10 percent. This is generally not a good thing with the itty-bitty pistols that are already hard to control, and that are so popular today. In most cases choosing a standard pressure load that has been adapted for short barrel use is a better option.

Do your own research, and your own testing – if possible – to determine if the gain in terminal performance is worth the increase in recoil and the wear and tear on your pistol? The effectiveness of a self-defense handgun, when used to shoot a human assailant, is mostly a product of shot placement and penetration. An extra tenth of an inch in bullet upset and the decreased shootability of the handgun might not be a tradeoff worth making.

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Plus-P ammo typically expands more quickly, causing it to skid to a quicker stop than might be expected. From what I read, one can't expect significantly deeper penetration as a result. But a quicker stop from a faster bullet means more energy delivered to the target, presumably doing more damage. But we can't know whether that extra bit of energy makes any difference in stopping ability. Until police reports start keeping track of whether a round used in a shooting is +P, we can only look at cavities in gelatin and guess. I use +Ps because my hands are large and I barely feel recoil. My 5-foot-2 wife, on the other hand, is recoil-sensitive and uses lightweight bullets at standard pressures. My guess is there's little difference in stopping power, but we can't know until someone establishes a database of actual shootings.
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