+P Ammunition

What is it and why use it?

by Mark Freburg

Most people think "+P" means more power, and while that is basically true, the "P" actually stands for pressure.  Thus +P stands for "plus pressure" or "increased pressure." 

Gas pressure, created by rapidly burning propellant (usually referred to as gun powder) is built up in a given cartridge upon firing.  This pressure is what propels the bullet out the barrel.  The maximum average amount of pressure a particular cartridge case and the guns chambered for that cartridge can handle is regulated by an industry organization known as SAAMI, for the Sporting Arms and Ammunition Manufacturer's Association.  After input from gun and ammunition makers and much testing, SAAMI specifies how much pressure a cartridge may produce.

Sometimes a given cartridge, especially one that has been around for a long time, is actually capable of being loaded to higher pressures than SAAMI has previously established.  For example let's consider the .38 Special, a cartridge more than 100 years old.   Many modern guns in this chambering can handle higher pressures than SAAMI originally set decades ago.  However, changing the set standard can't be done because of all the many older guns still in circulation which cannot handle any increased pressure safely.  In this case SAAMI establishes a second standard that they refer to as "+P." 

In our example then we have a standard pressure .38 Special cartridge and an increased pressure--or +P--.38 Special cartridge.  These can now be considered two separate cartridges.  Most older guns are safe to use only with (standard pressure) .38 Specials, while a modern gun may well be safe to use with either .38 Special or .38 Special +P.  Outwardly the cartridges are identical, with the only difference you can see being the headstamp, or marking on the rear of the cartridge, which usually will have the maker's name and the name of the cartridge.  If it is a standard .38 Special it will usually read ".38 Special" or ".38 Sp."  If it is a +P cartridge, "+P" will be added to the name.

Some cartridges have +P counterparts, some do not

There are several different cartridges for which SAAMI has established a second, higher pressure, +P version, including the .38 Special, 9mm Parabellum (aka 9mmP, or 9mm Luger), .38ACP, and .45ACP.  You will note all of these are old rounds that were created before WWI, and because of that pressures have been held down due to older, weaker guns in these chamberings.  Their modern counterparts are referred to as .38 Special +P, 9mm +P, .38 Super +P, and .45ACP +P.  Note the only one in which the name has changed is the .38ACP, which in high pressure guise is called the .38 Super +P.  Because of the use of "Super" instead of "ACP," many people refer to that round simply as the .38 Super, but it properly is the .38 Super +P.  There is no "standard pressure" .38 Super--the standard pressure version of the same cartridge is called the .38 ACP.

Note also that modern cartridges such as the .357SIG or the .40S&W do not have a +P counterpart.  There is no need.  These rounds were designed in the 1990s, and all guns made for them are equally modern, thus these two rounds are already as powerful as they can be.

What's good about +P?

What does a +P cartridge offer?  Increased pressure means increased power in the form of higher velocity.  Higher velocity means increased energy, or the ability to do work.  This in turn means a cartridge that may have a better chance of incapacitating an attacker more quickly than does a non-+P version of the same cartridge.  A +P round however cannot be thought of as a more powerful cartridge in general, but only when compared to its older standard pressure counterpart.  As an example, the 9mmP is a more powerful cartridge than the .38 Special.  In most cases, a standard 9mmP is still more powerful than even a .38 Special +P.

What's not good about +P?

There are two downsides to a +P cartridge.  It will have more recoil or kick than the standard version of the same cartridge when both are fired in the same gun.  It will also be harder on the gun.  Even if the gun in question is rated by the manufacturer to be suitable for +P ammo, the gun will wear out sooner.  The pressure of firing is what wears out guns, and the more pressure the more eventual wear.  Many people choose to use +P ammo for defense and standard ammo for practice for this reason.  If you do choose to go that route, be sure to practice with enough +P ammo that you know what it feels like to shoot, and you also know where it strikes the target compared to a standard pressure load.

If, on the other hand, you want to practice with ammunition of the same power you load for self-defense, then just be aware you may need repairs or replacement sooner than you would if using standard pressure ammo all the time.  How much sooner?  It's impossible to say because there are many factors that go into this including how well you otherwise maintain the gun, how often you change springs, and mostly--how often you shoot.  Even with lots of +P shooting most modern guns will last many thousands of rounds with no damage.

Should you choose +P ammo for yourself?

All I can offer you here is my opinion.  I think .38 Special +P should be chosen if one can handle the increased recoil.  A .38 Special is not a particularly powerful round, and while the +P version doesn't turn it into a .357 Magnum by any stretch of the imagination, every little bit helps. 

In 9mmP, +P is useful, but the only gun I use it in is a 9mm revolver.  Almost all modern 9mm pistols can also be had in .40S&W.  If you feel you need more power than the standard 9mmP offers, consider buying the same gun in .40S&W instead of 9mmP to begin with.

(Added, 2023: while many pundits will tell you the .40S&W is dead, ask yourself why they say that.  Has it changed since its heyday from the 90s to the through the teens?  No.  Guns and ammunition are still available.  If you can shoot it in the guns you choose, the .40 is still a more powerful round than the 9mm, as long as you choose carefully.  Be aware that some ammo makers have downloaded .40S&W ammo, so always check data and buy wisely.  If you are interested in this, see our article on the .40S&W here.)

.38 Super is one round where everyone will normally use .38 Super +P ammo, as .38 ACP ammo is obsolescent.  (Edited to add: And truth be told, most manufacturers have downloaded .38 Super +P ammo so that it is less powerful than it should be today, almost down to .38ACP levels. You have to search to find .38 Super +P ammo that is loaded to its true potential. The same is true for the 10mm Auto, which has been downloaded almost to .40S&W levels. There is no logic for this. .38 Super and 10mm shooters should look to Buffalo Bore and Double Tap ammunition for true, full power ammo in their respective calibers, as the big makers have sold them out. 16Mar13)

In .45ACP the difference in recoil between the standard round and the +P version really begins to be noticeable.  I don't use .45ACP+P in my .45ACP pistols and don't feel they are needed.  Again I must emphasize this as merely my opinion.  I certainly don't begrudge you increased power however and if you want it, test fire some +P ammo and decide for yourself.

Power versus controllability

At this point the only thing I would caution you on is not to go for power at the expense of controllability.  If using +P ammo makes the gun too difficult to control--to shoot rapidly and accurately--then +P may not be worthwhile.  If you have any questions on this topic, post a message to me on the forum's message board.

copyright 2006 by Mark E. Freburg