The Pluses and Minuses of +P Ammo

“These go to eleven.” – Nigel Tufnel 

We humans seem predisposed to want more. More time to shoot. More guns. More ammo to shoot (which, if we’re honest, is the reason for this site’s existence…), and more power from our ammo. We want our ammo to do it all. We want laser-like accuracy, low recoil, flawless functionality, and devastating impacts on the target. +P ammo was created with those last two items in mind. Let’s take a look at what it is and what it can do for you. 

At its heart, +P ammo is the same size and shape as regular ammo, but loaded so that it delivers higher pressures in the chamber when fired. This, in turn, leads to higher muzzle velocities and more energy delivered to the target. Those higher pressures place a higher strain on your firearm’s parts, which can lead to catastrophic malfunctions. The bottom line is, unless your gun has been specifically designated as being able to shoot +P ammo, don’t do it.  

The standards for +P ammo are set by SAAMI, the Sporting Arms and Ammunition Manufacturers’ Institute. SAAMI is an association of firearms, ammunition, and component manufacturers that lists out the standards for ammo and other products in the firearms industry. There is no set standard for how powerful +P ammo is compared to standard pressure ammunition. However, in general, +P ammo generates around 10% more pressure than standard ammunition, which in turn translates into higher muzzle velocities for +P ammo. SAAMI recognizes four different kinds of +P ammo: 9mm Luger +P, .38 Super +P, ..38 Special +P, and .45 Automatic +P. 

More Power, More Often

+P ammo has its roots in the transition from black powder cartridges to modern smokeless powder. Modern gunpowder is more efficient than black powder at turning itself into energy to move a projectile through the barrel. As a result, modern cartridges require less propellant to reach a given velocity than the equivalent black powder cartridge. This in turn means there is more empty space inside to pack in more gunpowder. Nature (and ammo manufacturers) abhors a vacuum, and thus +P ammo was born. 

The first factory-produced +P ammo was the .38 Super cartridge, created from the .38 ACP cartridge. John Moses Browning created the .38 ACP cartridge in the early 1900s for his M1900 pistol, giving it more punch than other cartridges available at the time. .38 ACP, it should be noted, is definitely not the same as .380 ACP. .38 ACP cases are 9mm in diameter and 23mm long, while .380ACP cases are also 9mm in diameter, but only 17mm long. .38 ACP will not fit into guns designed for the lower-powered .380ACP. More on this idea later. 

However, .38 Super has now fallen out of favor in the U.S., except for IPSC and USPSA competitions. The idea of an upgraded, up-gunned cartridge stuck around, though. .38 Special evolved into the much more powerful .357 Magnum round. .357, however, has a larger case than .38 Special, so guns that shoot .38 Special cannot shoot .357. This is different from +P ammo, which uses cartridges of the same shape and dimensions as standard ammunition.

Drawbacks to +P Ammunition

As you might expect, the extra power from +P ammunition also delivers more recoil. I could easily tell the difference between the normal strength ammo and the +P in our tests. The +P delivered more felt recoil to my hands, which meant more muzzle rise and more time needed to get the gun back on-target. 

In addition to this, the higher pressure of a +P round puts more stress on your pistol. This can lead to a rapid unscheduled disassembly of your gun (aka an exploding gun) in your hands. Not all guns are capable of handling the pressures of +P ammunition. Consult your owner’s manual if you are unsure if your pistol can hold up to +P ammunition. If the manual says that +P ammo is good to use in your gun, you should (SHOULD!) be okay to shoot it. Otherwise, stay away from +P and shoot normal pressure ammo instead.

Reasons to Use +P Ammo 

There are two reasons to use +P ammo in a defensive pistol. The first is to deliver more energy onto the target. The idea is that a faster round will penetrate deeper into the target, increasing its chances of making an incapacitating wound. The second, less well-known reason, is that more pressure in the chamber means that more energy is available to cycle your gun’s action. This, in theory, will decrease the chances of having a malfunction at a critical time and make your gun slightly more reliable. Let’s test these theories to see if they are true. 

We will be testing the effects of two different kinds of +P ammo versus their standard pressure counterparts, in two different calibers. The ammo we will be testing is Speer 124 grain 9mm JHP versus 124 grain 9mm +P ammunition. We will also test Federal .45 ACP HST JHP ammunition versus .45 ACP HST +P JHP ammunition. 

Our first test was comparing the muzzle velocity and muzzle energy of +P ammo versus the standard pressure ammunition. To test this, we shot 10 rounds of each of the 9mm standard and +P through a Glock 19. We also shot 10 rounds each of the .45 ACP standard and +P ammo through a Colt Competition 1911. We measured the velocity for all 40 rounds using a Competition Dynamics Prochrono chronograph placed 10 feet away from the muzzle. 

Velocity / Muzzle Energy Test Results

Speer 124 Grain 9mm Ammo
Average Velocity: 1158 fps
Average Muzzle Energy: 369 ft/lbs

Speer 124 Grain 9mm +P Ammo
Average Velocity: 1194 fps
Average Muzzle Energy: 392 ft/lbs

Federal HST 230 Grain .45ACP Ammo
Average Velocity: 863 fps
Average Muzzle Energy: 380 ft/lbs 

Federal HST 230 Grain .45ACP +P Ammo
Average Velocity: 911 fps
Average Muzzle Energy: 424 ft/lbs 

Both the 9mm and .45 ACP +P ammunition delivered higher velocity than their standard pressure counterparts. In addition to this, both rounds were close to the added 10% in velocity gained from using a +P round. But what does that added energy mean when the round hits the target?  

To test the penetration of +P ammo versus standard pressure ammo, we will shoot 5 rounds of each into a block of synthetic gel covered with four layers of heavy cloth placed 10 feet away from the muzzle. The ammo we’ll compare is Federal HST 230 grain JHP .45 ACP versus the same ammo, but in a +P loading. 

Penetration Test Results 

Federal HST 230 Grain .45ACP Ammo
Average Penetration Depth: 16.01 inches
Average Expansion: .82 Inches

Federal HST 230 Grain .45ACP +P Ammo
Average Penetration Depth: 15.7 inches
Average Expansion: .84 Inches

There was no functional difference between the standard pressure and the +P rounds. If I’m honest, these results surprised me a bit. Given their higher velocity, I was expecting more penetration from the +P rounds. However, I had a chance to ask this question to one of the ammunition designers at Federal Premium, and they said that +P defensive hollow points are actually less likely to overpenetrate. The faster velocity of the +P rounds makes the round “open up” quicker inside the target, bringing it to a halt in about the same space as a normal pressure round. 

Is +P ammo right for you? 

The answer to this question is based on a number of things. First off, unless your gun manufacturer specifically states that your pistol can handle +P rounds, shoot the normal pressure rounds instead. All that extra pressure from a +P round places more stress on your pistol’s chamber and barrel. Unless your gun is designed to handle that pressure, stick to the normal pressure rounds. 

Secondly, we are in a golden age of bullet design. Pistols once relied on just velocity to penetrate deep enough to cause a defensive stop. Now, however, with modern computer modelling and rigorous testing methods, today’s hollow point ammo can reliably penetrate deep enough for defensive purposes. 

We are also in a golden age of guns. This means that today’s guns are more reliable than ever before, and don’t need the extra pressure from +P ammo in order to be reliable. If you believe that +P ammo solves more problems than it creates, use it with confidence. However, if you’ve tested your defensive ammo of choice and are satisfied with how it runs in your gun, use that instead. Either way, it is up to you to get the hits when they matter the most. No amount of velocity or muzzle energy is going to make up for a missed shot.