When shopping for ammunition, you’ll find a wide variety of calibers outside of the norm, like the calibers we talked about in Handgun Caliber Names Explained. Alongside normal 9mm Luger, 9x19mm, or 9mm Nato ammo, you will see boxes that say they are +P. Simply put, 9mm +P are higher pressure rounds that develop more muzzle energy than standard rounds. You will of course find +P ammunition in other calibers as well. The higher muzzle velocity on the projectile creates a more powerful impact but also means there will be an increase in recoil.
You should always consult your owner’s manual before using +P ammunition in your firearm. If your handgun is older and you don't have a manual to consult or can't find confirmation from the manufacturer, then it's best to assume you should not use it. +P ammunition in a handgun that is not rated for it can have dangerous and catastrophic results. Some handguns are simply not designed for the higher-pressure loads making this combination of firearm and ammunition unsafe. If you can’t find this information, it is best to stick to standard pressure loads, which means avoiding +P entirely.
Now, back to why you would choose to use +P ammo. Aside from producing greater muzzle velocity, there are other factors to consider but for now let's just look at the velocity. A 9mm 124gr Federal® HST® has a muzzle velocity of 1150 feet-per-second (FPS). The same bullet in Federal HST +P has a muzzle velocity of 1200 FPS. A 50 FPS increase is only about 4% faster, but I’ve illustrated with the targets below how that small increase in velocity has a big impact on energy.
Now let's look at weight, the second key factor in the energy equation. You will see the weight of the bullet in grains featured somewhat prominently on each box of ammunition. Standard 9mm target ammo will most often be 115gr or 124gr. You might hear some people say that the heavier bullets have more energy or “stopping power”. In some cases that is correct, but it is not the whole story and often wrong if you don't consider all the factors. Energy or “stopping power” is a function of the mass of the bullet multiplied by the square of velocity. Velocity is determined by the powder charge used to propel the bullet. The +P charge on the 9mm HST I mentioned gains 50 FPS over the standard charge but remember that energy is a square of the velocity. That means for the same weight bullet we’re now multiplying by a much bigger number. Without detailing out the math, that standard 124gr HST with its 1150 FPS has 364 ft-lbs of energy. The 124gr +P HST has 396 ft-lbs, a 9% increase in energy for only a 4% increase in velocity.
Now let's look at what a heavier bullet does for energy. With a heavier bullet, the diameter and the overall length of the loaded cartridge has to remain the same to fit the magazine and chamber. That means extra weight must be on the bottom of the bullet which is seated in the cartridge. That means there is less room for powder in the case. For this reason, you generally won't see a 147gr +P, though some do exist. What you will usually find on the shelf is 147gr HST with a muzzle velocity of 1000 FPS. The bullet itself is 18% heavier than the 124gr, but it's now traveling 150 FPS or 13% slower. When you look at the result of the energy equation, the 147gr HST ends up with 326 ft-lbs, an 11% decrease in energy from the standard HST. The bullet has more mass, but it has a lot less energy because it can't reach the same velocity.
Another factor related to both the velocity and bullet weight you should consider is the expansion. Hollow-point bullets are designed to have controlled expansion which is caused by simple physics. The hollow point has seams designed to split like petals on a flower and curl back; these increase drag make the diameter larger. This does two things; it creates a larger impact point and dissipates energy to the target faster meaning the bullet will dissipate most of its energy inside the target. Generally speaking, the faster a hollow-point is traveling, the more it will expand. Think of throwing a water balloon, if you throw it slow, it may not break, or you just get a small splash. The same balloon thrown much faster splatters and sprays much wider. A bullet is obviously much tougher, but the same idea of expansion relative to velocity applies.
When it comes to ballistics, there is a lot to cover and a multitude of options to choose from. And as with all things, there are trade-offs… Choosing a +P round comes with higher recoil but better ballistic performance and more energy. What works for one person will not be the same for others; as with every aspect of firearms, you should test your options and decide on what works best for you.
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