In the world of firearms, there are about as many types of ammunition as there are types of weapons. Caliber, bullet weight, and type all go into making an informed choice about the type of ammo to run through your weapon. Let’s cover some of the basics.
CALIBER
A weapon’s caliber is the measure of the inner diameter of the firearm’s barrel. This is also the measurement of the outer diameter of a projectile, measured in hundredths of an inch or millimeters. There are many different calibers, but for the purposes of this post, we’ll focus on the common calibers, ordered by size (and, in most respects, power).
.22LR – This is one of the most popular calibers on the market, available in pistols and rifles. Small, cheap, and light recoiling, this round is ideal for training purposes, as well as plinking around the range. The .22 has been around since the 1800s. Its relatively low kinetic energy make it less than ideal for defense purposes.
.380 AUTO – The .380 Auto is the largest practical self-defense round that can be adapted to very small pistols. It was developed around 1912 by John Browning. This is the smallest caliber recommended for self-defense situations (keep in mind that shot placement is still critical).
.38 SPECIAL – This revolver round is likely the most popular ever produced. You’ll find anything from snub-nose revolvers to match competition guns designed for this caliber. Many consider .38 special to strike the perfect balance between accuracy, power, and recoil.
9MM – The 9mm round is known by many names, as it’s used all over the world. 9mm Para, 9mm Parabellum, 9mm Luger, 9×19, 9mm NATO, the list goes on. All of these are different names for the same round, so don’t let that confuse you. As far as defensive rounds are concerned, 9mm begins the truly practical bracket. The small cartridge size lends itself well to compact semi-automatic pistols without sacrificing power or capacity.
.40 S&W – This cartridge is a relatively new round, created in 1989. It strikes a middle ground between the 9mm and the heavier .45 ACP. Demand for this round has soared in recent years, and the .40 S&W has been adopted as the default caliber for many law enforcement agencies. Its blend of power and accuracy make it a very handsome option for self-defense shooters as well.
.357 MAGNUM – The .357 Magnum is the most attractive revolver round for self-defense. This caliber has excellent power for its size, and is very common. Worth noting is that the .357 Magnum and the .38 Special are the same caliber, but the .357 uses a longer case. What does this mean? When you buy a revolver in .357, you’re really buying two guns in one, because the .357 revolver will also fire .38 special. However, this is a one way street. .357 rounds will not fit in a firearm designed for .38 special, as the cases are too long.
.44 MAGNUM – Ah, the Dirty Harry. The .44 Magnum is an extremely powerful revolver round, but generally unsuitable for self-defense. As I mentioned in Firearms Laws, over penetration of your target needs to be considered, and the .44 Magnum has so much power, there’s a good chance your projectile will penetrate straight through your intended target and into innocent bystanders. This caliber was designed for hunting, and it excels in that regard.
.45 GAP – I mention .45 GAP to clear up any confusion between it and .45 ACP. .45 GAP (Glock Automatic Pistol) was requested by Glock, because they wanted the ballistics of the .45 Auto without the large size. What resulted was a .45 caliber cartridge with a smaller case. While Glock was successful with the cartridge, it never really took off, and there are few pistols chambered for it, namely the Glock 37. These rounds will not chamber in a .45 ACP or .45 Auto firearm, as the GAP cartridge is shorter.
.45 ACP – ACP stands for “Automatic Colt Pistol”. Keep in mind that .45 ACP and .45 Auto are the same cartridge. .45 was the go-to caliber for the military for a number of years due to its inherent power. Out of all the recommended self-defense calibers, the .45 carries the most energy, but because of its large size, firearms have to sacrifice magazine capacity to stay easily concealable.
BULLET WEIGHT AND TYPE
A bullet’s weight is measured in grains. One grain is equal to about 65 milligrams. Different calibers use different weights of bullet, with the trend being larger calibers having heavier bullets (for example, the 9mm caliber generally uses bullets between 115 and 124 grain).
Heavier bullets carry more kinetic energy at a slower velocity but are higher recoiling, while smaller projectiles can be pushed to higher velocities for better external ballistics and have lower recoil. Kinetic energy can be considered the wounding potential of a projectile, while external ballistics is the science of a projectile’s trajectory. External ballistics becomes incredibly crucial once we start shooting with long-range rifles. In a handgun, particularly one used for concealed carry, kinetic energy is more important.
What does this mean for the shooter? Well, once you’ve chosen your caliber, you’ll want to look at two different types of ammunition, training ammo, which is inexpensive, typically FMJ, and a light bullet weight, and carry ammo, which is costly, usually hollow point, and heavier.
Let’s talk about FMJ and hollow point for a moment. These are types of bullet, and they differ greatly. FMJ, or full metal jacket rounds are lead bullets that are covered in a shell of harder metal, usually copper, like so:
There are a number of advantages to FMJ bullets. The lead is encased by another metal, which means you don’t have to worry about spraying dangerous lead particles around every time you hit a target. Additionally, they offer better ballistics than hollow point rounds, which makes FMJ great for practice or target shooting. FMJ is also generally cheaper. However, nothing is without drawbacks. Full metal jacket bullets make poor self-defense rounds. They are not designed to expand on impact, which means they have a higher chance to fully penetrate your target and keep sailing. Thus, we have hollow point rounds.
Hollow points are specifically designed for self-defense. These bullets, as you can see, have an opening machined into the front. On the left is a hollow point round after hitting a target. They are designed to expand, or mushroom, once entering a soft target. These rounds are meant to STOP in whatever you shoot them at; the mushrooming effect acts much like a parachute, slowing the round very quickly and decreasing the risk of over-penetration into a bystander. Hollow point rounds are also more likely to bite into impact surfaces, making dangerous ricochets less likely. This is what you’ll want for your defensive ammunition, the rounds you carry when your pistol is strapped to your side, the rounds you’ll use to defend your life. Generally speaking, they are heavier bullets, and also more expensive. There are a myriad of different designs from many different manufacturers.
When choosing your ammunition, I recommend buying one box from a few different manufacturers and seeing which ammo you and your gun likes best. Not all firearms reliably shoot all types of ammo. My XDm, for example, loves Federal American Eagle, but has issues with Blazer Brass. Find out what works for you. When you settle on a carry ammo, fire at least 100 rounds of it through your weapon to get used to the way it handles and make absolutely sure that it feeds reliably in the gun. Your life may depend on those rounds, and you want to make sure they’ll function as planned when you need them.
Until next time, have fun, stay safe, and shoot straight!
The New Caliber 
I recommend you edit the paragraph on jacketed hollow points. They are recommended for use in personal protection firearms, not because they, as you wrote, “create a significantly larger wound.” They are recommended for the same reasons why law enforcement use them: the mushroom shape actually acts a bit like a parachute (an analogy I picked up from reading Massad Ayoob’s prolific intellectual output) and slows the bullet down so that it will not over-penetrate the target to hit a partner or bystander. Also, the shape of the bullet bites into surfaces more readily than FMJ bullets and is therefore less likely to ricochet and injure innocents. In the aftermath of a contested righteous self-defense shooting, ignorant or sleazy lawyers would use your comment against you in their trial tactics.
Also, with regard to .45 ACP, I’d mention that.45 AUTO is the same, but not .45 GAP. Also, the military still primarily relies on .45 AUTO, because the Hague Convention of 1899 bans lawful combatants from using “bullets which expand or flatten easily in the human body, such as bullets with a hard envelope which does not entirely cover the core, or is pierced with incisions.” That’s not to say that MPs and SPs aren’t able to legally use JHP rounds for internal base security operations, but I don’t whether that is a common practice.
LikeLike
Edited to include your comments. I appreciate the critique Janine, you bring up some good points I hadn’t considered.
LikeLike
We’ve all got to look out for one another. I like what you’re doing with your blog. :-)
LikeLike