Ammo Explained

When people talk about self-defense firearms, they often focus on what caliber it fires and pay little attention to what type of bullet is actually going down the barrel. There are several reasons why one person’s .45 caliber pistol will not be as potent as another person’s .380 caliber pistol, and I will explain why.

Components of a Round

But before we can get into sizes, we must understand the different components of a round.


A piece of metal that travels down the barrel and is the actual projectile.


Made of metal or plastic (usually brass) and which holds all the other pieces of the round together.

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Burns quickly and produces a large amount of expanding gasses which seek the path of least resistance, which is to push the bullet down the barrel of the gun.


Used to eject the spent round.


A small explosive that is detonated when struck. It ignites the gunpowder.

Let’s Talk Dimensions

So, with an understanding of what makes up an actual round, we can start talking about the dimensions. When a cartridge, or round, is described, there are two dimensions that must be understood. For example, there are several types of .45 caliber rounds. There is the .45 ACP (Automatic Colt Pistol), which is the most common these days, and the .45 LC (Long Colt). The .45 tells us that the diameter of the bullet itself is .45 inches. The length of the case is the second dimension, which for the .45 ACP would be 23mm, while the Long Colt would be 32.6mm. Sometimes it is easier to know the length of the round because that is how they are labeled, such as 9mmx18mm and 9mmx19mm. Other times however, it is difficult to see that two rounds are even in the same family. The .380 ACP is also a 9mm round (9mmx17.3mm). The length of the brass matters because the longer the brass, the more gunpowder can be used. The more gunpowder behind the bullet, the faster it travels, and speed increased energy on target.

Bullet Types

Now that we know there are two dimensions to be considered, we can look at bullets types. There several different bullet types that can top your chosen brass and that can be a bigger difference than the caliber itself. How can that be true? A smaller bullet moving at a slower speed will not have as much energy as a larger bullet moving at the same speed or faster… but if a bullet passes all the way through the target and keeps moving, not all of that energy is delivered to the target. A bullet that expands when it hits the target and stops moving inside the target delivers much more energy.

So then, if an expanding bullet that delivers all of it energy to the target is more effective than one that keeps moving, how do we get the more effective, expanding bullet? We have to select bullet types that are designed to do just that, and there is a whole mess of bullet types:

Full Metal Jacket (FMJ)

An FMJ round is a lead bullet wrapped in copper, with the exception of the underside of the bullet. This round is fast moving, accurate, and punches through objects like brick and drywall very well, but does not expand and has a tendency to travel through targets with the potential to strike object down range. Because of that, we know that this type of round will not deliver all of the energy it has available.

Total Metal Jacket (TMJ)

This bullet is much like the FMJ except the entire bullet is wrapped in copper, including the base, which causes it to function much like the FMJ. It is used when there is an expectation of having to shoot through heavier or multiple obstacles. So, again, this round is not that great for stopping a threat and imposes the risk of traveling further than desired.

Soft Tip (ST)

A soft tip round is one of the original hunting rounds and is also known as a partial jacket. It is a lead bullet with a copper jacket that does not come all the way up, leaving the tip as soft lead. This bullet can maintain a shape at the base, making able to punch deep into a target, but the soft tip expands and allows it to shed more energy to a target, thus giving it more stopping power. The problem with these rounds though, is that it is hard to control when the bullet will expand in the target, or if it even will at all.

Jacketed Hollow Point (JHP)

Hollow Point rounds are lead bullets that have a hollow tip, shaped much like a bowl, and a copper jacket that comes up to the edge of that bowl. These rounds allow for a deep punch, much like the ST, but the timing and rate of the expansion in better controlled. They have one flaw though. The hollow tip can get clogged with clothes and flesh, causing it to act much like a FMJ round.

Critical Defense

There are many types of manufacturers that have their own term for these types of rounds, but the principle is the same. It is a JHP bullet with a rubber or polymer ball or tip placed into the hollow cavity. This tip allows the round to enter a target deeply before the tip breaks. Once the tip breaks inside the target, it allows the cavity, or hollow point, to expand and deliver an amazing amount of energy to the target.

There are many, many more types of bullets out there, all designed for a specific purpose, making a list much too long to be explained here. However, the most common rounds found in self-defense guns have been covered and should paint a picture of what should be looked for in a defense type bullet.

How Cartridges are Measured

So, now that we understand the bullet types and how cartridges are measured, we can see that size is not everything. A 9mm Parabellum, which is what the US Military shoots, is a 9mmx19mm cartridge. This round has a longer brass than the .380, which is a 9mmx17.3mm round, which means that the mass of the bullet is about the same, but the Parabellum is moving faster, which creates more energy. So how can my .380 be more effective than your 9mm Parabellum? If you are shooting FMJ rounds and I pick up critical defense rounds, then I will be able to deliver all 190 foot-pounds of energy to a target while you will waste 200 foot-pounds out of your 340 available foot-pounds.

But no matter what caliber you choose, buy quality ammunition designed for the task at hand and learn to shoot straight.


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