Is +P Ammunition Safe? What You Need To Know About Overpressure Ammunition

Is +P Ammo Safe To Use In My Gun?

You might have heard a few things about +P ammo and it's relative safety or unsafety in firearms. Maybe you've been told you have to carry it in order for ammunition to be effective.

We're going to clear those things up for you.

Correct use of ammunition, of course, is a vital part of , and for the newbie or beginner, the issue of overpressure ammunition might seem a little daunting.

That's okay! We all start somewhere. We're going to go over what +P ammo is, whether it's safe or not, and so on. Hopefully, you'll understand why it may not be a good idea to use in your gun, or why it might be totally no big deal.

What Is +P Ammo?

So, to start off, +P ammo is "overpressure ammunition" as the "+P" designates added chamber pressure.

So, how a gun works is an explosion is set off behind a projectile. (The bullet.) The bullet is slightly larger than the barrel (technically the bore, but whatever) forming a seal. The explosion builds up pressure behind the bullet and squeezes it out of the barrel toward the target.

Now, various cartridges and calibers are designed for certain pressure levels. The designer came up with a recipe to send a particular projectile downrange at a particular speed, which creates a certain amount of pressure inside the chamber.

In the case of, say, 9mm it's about 34,000 psi, in the case of .45 ACP it's about 21,000 psi and in the case of .30-06, God's own rifle cartridge, it's around 60,000 psi.

Now, the governing bodies that set measurements and so forth for ammunition (SAAMI and the CIP) mark down those pressure levels as one of the defining characteristics of what makes a particular cartridge that cartridge.

If you put in a bit more powder, it creates additional chamber pressure as well as propelling the bullet a little faster.

But how much more pressure does +P ammo add?

Generally, about an extra 2,000 to 3,000 psi. That's it. Those same bodies (CIP and SAAMI) also maintain standards for overpressure loading, and they allow for an extra 2,000 to 3,500 psi of chamber pressure.

But is that extra 2,000 THE STRAW THAT KABOOMED THE CAMEL'S GUN?!?!

Actually...no.

Proof Loads Vastly Exceed +P Ammo Chamber Pressure

Part of manufacturing firearms is that each individual gun must be proofed before it leaves the factory. What that means is the chamber is subjected to a WAY overpressure powder charge to prove the barrel and chamber are sound.

Now, what proof loads establish is that the barrel and chamber are more than strong enough for the stresses of standard pressure loadings.

Think of it this way: a car with 100 horsepower will struggle a bit on hills and getting up to highway speed. A car with 450 horsepower will not.

Proof testing ensures that a gun can handle more chamber pressure than they will typically be subjected to.

Now, what are proof load chamber pressures like?

To give you an idea, a 9mm proof load is typically around 48,000 psi (47,500 psi for NATO spec and around 50,000 psi for SAAMI specifications for 9mm proof loads) and, again, barrels have to be proof-tested before leaving the factory.

Given that 9mm+P runs around 38,000 psi...that's not a big deal.

Except...that sometimes it is.

We're going to go over when and how overpressure ammunition can be unsafe/bad for your gun, as well as why manufacturers recommend you either don't use it or only do so sparingly.

However, what we're also saying here is that +P ammo is not inherently dangerous, provided it's loaded to standard specification for +P ammunition and used safely. If you were loading your carry gun with +P before putting it in your ...it's fine, though with some exceptions.

But what are those exceptions?!

Where +P Ammo Can Cause Problems

So, the issue with +P ammo is not so much that it's inherently unsafe. It's not; proof-tested firearms leave the factory able to cope with the additional chamber pressure....generally.

Potential issues arise in two areas.

First, we have when +P is used in semi-automatics.

So, how a semi-automatic firearm works is that the detonation of the cartridge sends the slide back, compressing the recoil spring. When the spring fully compresses, the slide returns forward.

In order for the gun to cycle correctly, the recoil spring is set to a specific tension so that the slide doesn't cycle too fast nor too slowly. This is the spring rate, just like how a shock absorber of a car is set to absorb shocks and vibrations from the road.

The faster the bullet leaves the barrel, the faster the slide travels backward. The faster the slide velocity, the stiffer the recoil must be to compensate.

Ammunition is part of balancing that function, and manufacturers tend to calibrate pistols with standard-pressure ammunition.

Since adding additional pressure increases the slide velocity, that can batter the frame and slide at the end of travel as well as increase the dwell time (when the slide is open) in between, which can potentially impact feeding and extraction.

Case Head Separation And The Glock Kaboom

The other potential issue is due to what's called "case head separation." This is not a common issue, but has been known to occur.

The cause is several-fold, typically due to a fault in the cartridge case in conjunction with the design of the feed ramp and chamber in some guns.

So, the material used in making a cartridge case can stand a certain amount of pressure. If the material is weak, due to imperfection or re-use by a handloader, the cartridge case may split before all the gas created by propellant ignition is expelled down the barrel.

Typically, the weak spot is in the web of the cartridge case near the case head, which is the rim and primer pocket.

Now, most modern pistols have a feed ramp. The bullet is pushed up the ramp and into the chamber.

Some guns don't fully seat the cartridge in the chamber; the case head is exposed inside the chamber. This matters as a fully supported case puts additional material under the case head, providing reinforcement and thus preventing a case head separation.

Why does this matter with +P ammo?

In a pistol that doesn't have a fully supported chamber, cartridge cases with weak case webs can rupture, causing case head separation and potential detonation of the pistol.

This type of failure is precisely the phenomenon called the "Glock Kaboom," which was known to occur in Glock pistols chambered in , .45 ACP and 10mm.

Granted, how likely is that to happen? Not terribly; case head separation, even in pistols without a full-supported chamber, are rare. However, it is known to occur from time to time.

Other Rare Issues With High Pressure Ammunition

There are some other known issues with higher pressure and/or overpressure ammunition, in select cases.

Some magnum revolvers are known for issues shooting a high volume of full-power cartridges. This is especially true for medium-frame (S&W K-frame, Colt L-frame such as Python and Trooper revolvers) pistols in .357 Magnum and older large frames in .44 Magnum.

Typically, the "issue" in question is a warping of the cylinder walls if the user feeds the gun a steady diet of .357 Magnum and/or .44 Magnum. This was due to insufficient material in the cylinder walls or inadequate heat-treating.

This was a known quantity at the time; magnum revolver aficionados such as Elmer Keith, Jeff Cooper and others held that the typical Colt or S&W was good for about 1,000 rounds of the hot stuff until replacement was necessary.

Modern revolvers, however, do not have this issue; Smith and Wesson, by the 1990s, was heat-treating and reinforcing their magnums. Ruger replaced their Security Six line altogether with the GP100, which has no issues with a spicy diet.

Colt also took steps to address this problem by going bankrupt and not making revolvers for more than 20 years. New production King Cobra and Python revolvers don't have any reports of accelerated wear due to using too much .357 Magnum...but they're relatively new guns.

Another related issue concerns Colt Delta Elite pistols, which are a 1911 chambered in 10mm. Early models of the pistol were known for developing a stress fracture in the frame with enough use of 10mm ammunition loaded to original specification, ie the 10mm Norma load.

That issue has also been addressed; Colt started making a relief cut in the frame where the stress fractures occurred. Look for a square notch above the controls in the grip area; the current models have it as well.

1911 pistols in 10mm from other brands may not have this feature, so bear that in mind if you intend to shoot full-power 10mm.

It is also the case that you shouldn't shoot .45 Super loads in a standard .45 ACP pistol. While some are rumored to be rated for it, that isn't the case; the springs are almost certainly not.

For those unaware, .45 Super is an overloaded .45 ACP cartridge, which generates about 28,000 psi of chamber pressure and propels .45 ACP bullets to full-power 10mm velocity and energy levels. However, it uses the same case as .45 ACP, just with thicker case walls.

.45 caliber pistols must be converted to .45 Super use, or else case head failure is a very possible outcome. The recoil spring, mainspring and firing pin spring must be changed at minimum, if not far more than that.

So Is +P Ammo Safe To Shoot

Is +P ammo safe to shoot? If you go by the numbers...yes, with some caveats.

It is well within the tolerances of modern firearms and certainly within the pressure level created by proof loads which modern guns are tested with. Therefore, it's "safe."

But that doesn't mean you should.

The slide and frame take more of a battering, and since the spring rate of the recoil system is developed for use with standard-pressure ammunition...it's not meant to do so on a regular basis.

Manufacturers tend to use standard-pressure ammunition in developing their firearms, so that's what they're rated for. If you use +P ammo, you do so at your own risk.

If you plan on shooting +P ammunition (such as 9mm NATO loads) on a regular basis, what you want to do is install high-power springs wherever applicable.

You'll need a stronger recoil spring, and most likely an upgraded firing pin spring and mainspring (if applicable) too. The stiffer springs will change the spring rate so the extra slide velocity is compensated for.

If you intend a far more limited diet of +P, meaning only occasional use...you have no need to worry.

However, +P+ ammunition...is another story.

+P ammunition is regulated by SAAMI and the CIP; they are manufactured to their pressure specifications and therefore are not unsafe. +P+ loads, however, are not; the manufacturer is completely in the driver's seat and it's unknown what pressure level may be generated.

Therefore, shooting or carrying +P+ ammunition is something of a crapshoot. If you carry a 9mm, and feel like you need +P+, a better idea is to just get a pistol in .357 Sig or .38 Super.

It is also the case that older firearms may not be able to tolerate +P ammunition, especially revolvers and older semi-automatics. Therefore, stick to standard pressure loads with older guns.

Is Using +P Ammo Even Worth It?

Since +P ammo is a little hotter than standard pressure, beats up the gun more and is more expensive (it should be said) at some point it begs the question of whether it's worth it or not.

First, the most reliable predictor of efficacy is and always has been shot placement. Any bullet works when placed correctly. Second, +P ammunition rarely adds more than 100 fps of velocity...when it does.

Additionally, it must be stated that handgun calibers' effects on the human body...are greatly exaggerated. A bit more powder doesn't change that.

Part of the belief regarding use of +P ammunition being necessary stems from the 1970s and 1980s. The dominant hollow point designs of the day (cup and core) were known for easily clogging in clothing and not sufficiently penetrating tissue and certainly not barriers.

This was especially true for 9mm; as a result, many officers stuck with .357 Magnum or .45 ACP pistols if allowed. A bad bullet at high velocity works better, as does a bigger bad bullet.

However, just as hunting ammunition had its great leap forward with Bitterroot Bonded and Nosler Partition, handgun ammunition did as well with the advent of modern bonded hollow points.

Standard pressure loads with modern hollow points in 9mm and other calibers have established themselves as more than reliable enough for defensive use.

It's worth noting that the FBI and the US Army selected Speer Gold Dot G2 147-gr JHP in standard pressure as a duty round, and many police agencies issue Federal HST 124-gr JHP in standard pressure.

It's up to you whether or not you want to use it. If so, do so safely and responsibly.