p ammunition

All About Plus P Ammo and Using It

When it comes to ammunition for defense purposes, one of the most constant recommendations is to use +P ammo. There is some discussion about whether plus P ammo is necessary or advisable to use in some firearms, which may give some people pause about whether use is prudent.


This kind of ammunition is very popular among both police but also concealed carriers, as it is very popular as self-defense ammo.


Plus P Means Overpressure


plus p ammunition

"Plus P" ammunition means "overpressure." This involves a little bit of basic science.


So, how a bullet works is fairly simple. The hammer/striker/firing pin sets off a primer, which is a tiny explosive charge, which in turn ignites a larger charge.


When the main powder charge (called "propellant") is ignited, this creates a small explosion inside the cartridge. This creates a huge amount of pressure inside a small space. Pressure in any enclosed space looks for any way out it can find, so the pressure inside the enclosed space can reach the same pressure as the ambient pressure outside it. (Nature abhorring them vacuums.) This causes the bullet to fly out of the barrel toward.


What does this overpressure do? Increases in pressure result in increased velocity. Ergo, the higher the pressure, the faster a bullet flies.


A lighter bullet can help as well, which is why a 115-grain 9mm bullet is faster than a 147-grain bullet, and this is also why many +P loads do and don't employ lighter projectiles. (Either to maximize velocity or get more velocity from a heavier projectile.) A similar concept is employed by necked-down rifle cartridges; a normal load for a larger cartridge can produce a very fast, flat-shooting bullet when the case is necked down to fit a smaller projectile, such as the .270 Winchester, which is made by necking down a .30-03.


The short version is more powder more pressure, making the bullet fly faster.


Using Plus P


using plus p ammunition

That said, each specific cartridge - and more importantly, the firearms that fire them - are designed to tolerate specific pressure levels, which plus P ammunition can exceed.


The Sporting Arms and Ammunition Manufacturer's Institute, or SAAMI, maintains weights and measures, if you will, for guns and bullets. That includes pressure ratings for cartridges. Basically, they set the bar for what ammunition is +P and what ammunition isn't +P.


For instance, SAAMI rates the 9x19 Parabellum (good old 9mm) maximum chamber pressure at 35,001 PSI, and 9mm +P at 38,500 psi. Anything over +P ratings is +P+, which is a whole other can of worms.


Why is this important? Higher chamber pressures exert greater wear and tear on the chamber and any moving parts. (The pressures actually stretch the metal.) Semi-automatic pistols can even fail to cycle with overpressure ammunition, if not suffer catastrophic failures in some cases. Even revolvers, including the large magnum revolvers, are susceptible to damage as well, unless - like some Ruger revolvers - they are engineered for higher-than-normal chamber pressures.


Granted, shooting .38 Special +P in a .357 Magnum is perfectly fine, as .38 Special +P generates far less chamber pressure than .357 Magnum.


Depending on your make and model of pistol, +P ammunition may be recommended only in limited servings, may be completely fine, or the manufacturer may strenuously advise that it never be used. Heed these warnings, as the people who engineered the gun to begin with know better than you do.


Is +P Ammunition Worth It?


is plus p ammunition worth it

Is it worth buying +P ammunition? Is it really that much better than a JHP load within normal pressures?


There's a certain amount of evidence to suggest so. Police departments have been using and continue to use +P (some even use +P+) loads as duty ammunition. Iif it's good enough for the professionals, it's good enough for civilians.


However, a certain amount of ballistic testing has shown that standard pressure rounds work just as well as some +P rounds and are perfectly capable defense ammunition, without needing to put greater strain on your firearm than necessary.




Sam Hoober 

About The Author


Born in southeastern Washington State, Sam Hoober graduated in 2011 from Eastern Washington University. He resides in the great Inland Northwest, with his wife and child. His varied interests and hobbies include camping, fishing, hunting, and spending time at the gun range as often as possible.

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