If you’ve recently taken up learning about home defense pistol shooting, or perhaps if you are a seasoned shooter that hasn’t messed with different ammunition much, you may not understand what +P ammunition is. Maybe you’ve never heard the term at all! There are some definite benefits from shooting +P ammunition, but first, let’s explain what +P is.
First of all, there are a lot of types of ammunition out there that may be called +P, whether by shooters in error, or even made by reloaders at home, but the technical definition of what truly constitutes +P ammunition is defined by SAAMI, the Sporting Arms and Ammunition Manufacturer’s Institute. SAAMI is a quasi-governmental body that publishes standards for ammunition chamber pressures, among other things, and attempts to keep ammunition standardized, which is a good thing. Realize that incorrectly loading your weapon with ammunition that is rated at a higher pressure than recommended by SAAMI is dangerous, and could be lethal in the worst cases. SAAMI, therefore, sets standards for same-chamber pressures and other standards so that both ammunition manufacturers and shooters can enjoy safe yet effective ammo.
Each caliber of ammunition has its own standard for pressures, yet SAAMI also has a published standard for ammunition with elevated pressures called +P. +P ammo, in that case, is ammunition that is loaded to modestly greater but still safe pressures for most firearms. Note that we said most firearms – it’s important to note that +P ammunition should never be fired from excessively old guns, or weapons in poor repair. In fact, +P ammunition should only be fired in weapons specifically listed by the manufacturer as being capable of firing +P ammo.
So how much pressure are we talking about? The chart below shows what typical +P loads generate over standard:
.38 Special — 17,000 psi standard pressure. 20,000 psi +P pressure.
9mm – 35,000 psi standard pressure. 38,5000 psi +P pressure
.45 ACP – 21,000 psi standard pressure. 23,000 psi +P pressure.
Certain manufacturers have taken to labeling some of their ammunition as +P+, but SAAMI does not have such a standard, nor does it publish standards for ammunition loading above +P. We can see from the above table that the gains in pressure are relatively modest, all things considered, which should dispel the notion that +P loads are an order of magnitude over standard loads — they’re not.
So what’s the point of +P ammunition, in that case? What is to be gained by increasing the pressure of the load? The gains can more or less be summarized in a single word – velocity. A +P loading is directly manifested in increased bullet velocity, which, in simple terms, translates to greater potential energy and stopping power. While a +P load will not turn a regular cartridge into a magnum, it does increase the velocity of the projectile enough to have noticeable gains in the energy department. And this is fundamentally the beauty of +P ammo – you can take the handgun you already have, load it with +P ammunition, and get a little more oomph out of the gun without any modifications whatsoever, assuming the gun is capable of firing it. If you want to get an idea of how much velocity a +P load imparts where the rubber meets the road, have a look at the table below:
.38 Special – 850 fps standard velocity. 945 fps +P velocity.
9mm – 1,140 fps standard velocity. 1,200 fps +P velocity.
.45 ACP – 1,015 fps standard velocity. 1,140 fps +P velocity.
Again, the numbers show a modest increase in velocity across the board. Note that for simplicity’s sake, we’ve not referenced the bullet weight in grains; different bullet weights will have an effect on the velocity of the bullet, and there are also +P loadings in the same caliber for different bullet weights. However, generally speaking, expect greater velocity out of a +P load compared to a standard load, bullet weights being identical. A multitude of tests have been performed that show that given two bullets of identical weight in grains, the one traveling at the higher velocity will impart more kinetic energy (i.e. stopping power) against the target. This is no mystery – it’s plain physics.
From a self defense standpoint, any advantage you can gain over an intruder or attacker is one you should take. +P loads are often (but not always) coupled with jacketed hollow point construction, making for a very effective defense round. The combination of increased velocity coupled with aggressively expanding projectiles makes for a combination that’s hard to beat. +P ammo does have a downside, however. For weapons that can’t shoot it due to age or design, it’s utterly useless and potentially deadly. It also has a substantially increased cost over standard ammunition, even though the corresponding increase in velocity is modest. This leads shooters to group ammo into two categories: plinking ammo, and defense ammo, and these categories are mainly thought of in terms of cost. Still, the decision to use +P ammo makes lots of sense when important factors such as the ability to stop attackers in as few shots as possible is considered. For defensive ammo, +P is definitely the way to go.