Ammunition Demystifier - Overview

Using the wrong ammunition in your firearm is extremely dangerous. You must know the proper ammunition for your firearm. The owners manual that comes with your firearm will tell you exactly which ammunition is safe for your firearm to shoot and many manufacturers make the manuals available online as well. The caliber may also be stamped on the barrel of your gun. You can verify the caliber of our ammimtion by checking the bottom of the round where it is typically stamped as well as the ammunition box. 

Ammunition - a word filled with mystery. When I began my journey into firearms, this subject and the overwhelming confusion that it created was almost enough to stop me in my tracks! I am one of those people that just dives in and consumes information relentlessly until I capture from it what I need, and I was beyond confused. What I have come to understand is that it IS confusing! As a woman, I am not incapable, in any sense of the word, of figuring it out, (which was what I started thinking when I began researching ammunition!) what I am however is practical. I want to know what I need to know and what it means for me, for my firearms and for my safety. I will try here to demystify and bring into clarity, the basics of what you need to know in regard to defensive ammunitions, .380, 9mm, .38 Special, .357 Magnum, .40, .45 calibers. There are many other calibers than what will be discussed here so I have provided links on the bottom of the page for those who would like to go deeper into this subject.

Let's start with some basics


Ammunition: the projectiles with their fuses, propelling charges, or primers fired from firearms


The basic components of ammunition are the case, primer, powder, and projectile(s). Shotshells have an additional component called wad.


  • Case: The container that holds all the other ammunition components together. It's usually made of brass, steel,copper, paper, or plastic.
  • Primer: An explosive chemical compound that ignites the gunpowder when struck by a firing pin.Primer may be placed either in the rim of the case (rimfire) or in the center of the base of the case (centerfire).
  • Gunpowder: A chemical mixture that burns very rapidly and converts to an expanding gas when ignited. Modern smokeless powder will burn slowly when ignited in the open (outside of the case). Black powder is less stable and can be explosive when ignited in the open.
  • Projectile: The object(s) expelled from the barrel. A bullet is a lead projectile fired through a rifle or handgun barrel. A slug is a lead projectile fired through a shotgun barrel. Shot is a group of lead, steel, tungsten, or bismuth pellets fired through a shotgun barrel.
  • Wad: A seal made of paper or plastic separating the powder from the slug or shot in a shotshell. The wad prevents gas from escaping through the shot and  holds the shot together as it passes through the barrel.


Round or Cartridge: The correct and accurate name(s) for the "entire package". It is not accurate to use the word bullet, as the bullet is one of multiple components.

Bullet: The bullet is actually just the pointed top or tip that you typically think of when you picture a round. A shotgun round does not have an actual "bullet" inside. It has either buckshot, a lot of little round pieces or a "slug" which is shaped like a bullet.

Caliber: 1) The diameter of a bullet or other projectile, 2) the diameter of a bore of a firearm usually expressed in hundredths or thousandths of an inch and typically written as a decimal fraction, i.e. .380 caliber, .45 caliber, sometimes in the metric scale i.e.. 9mm. It is important to performance that a bullet should closely match the diameter of a barrel to ensure a good seal.

Gauge: The term "gauge" describes bore diameter of a shotgun, but unlike "caliber" used for handguns and rifles, the larger the number, the smaller the bore.

Centerfire Ammunition: Ammunition in which the primer is located in a small cup in the bottom center of the case.

Rimfire Ammunition: Ammunition in which the primer is located in the bottom rim of the case. Typically, rimfire rounds are smaller calibers than centerfire rounds.

Hollowpoint: A metal jacketed cartridge design with a concavity in its nose to increase expansion on penetration of a solid target. Some hollow-points are also designed to fragment as they expand. They are least likely to over-penetrate the target and harm an innocent bystander. Commonly used for self-defense

Softpoint: A metal jacketed cartridge design in which the nose of the core of the bullet is exposed to ensure the expansion of the bullet upon impact. Often abbreviated "JSP" or "SP." They tend to expand more slowly than a Hollow Point bullet and are used where deeper penetration and expansion are needed.

+P or +P+ Ammunition

"Plus P" or "Plus P Plus" mean that the cartridge is loaded with a higher pressure than standard ammunition. This gives your round more firing power and a greater impact on your target.You can see whether or not your ammo is +P or +P+ on the cartridge box, or sometimes it's stamped on the base of the cartridge. +P or +P+ cartridges are usually center-fire cartridges.


Grain is the actual weight measurement of the bullet component of a cartridge, not the entire cartridge. The more it weighs, the more grain it has. Standard weight for .45 ACP ball ammunition (full metal jacket - FMJ) is 230 grain. Standard for 9mm is around 115 grain.

Note: There are many inconsistencies in ammunition manufacturing so this number does not always reflect the actual diameter of the bullet and in some cases the metric scale is used. In some cases a second number is given usually representing the bullets length and letters (abbreviations or words) will then follow to complete the name of the cartridge. This entire "name" is important and you will need to know the entire description, including the letters.

What Is FMJ, JSP, JHP?

Yes, sometimes letters are added to the name to differentiate and describe rounds. These letters describe how the round is "packaged". Every minute detail of a round effects how it performs, so naturally in what and how a round is packaged matters in how it will perform. I did tell you it was complicated, but no too complicated. I promise you will get it and will be able to approach a shelf of ammunition with confidence!

FMJ is "Full Metal Jacket" and is used to describe rounds that are entirely encased (except for the bullet base, typically) in a metal jacket, usually copper alloy called gilding metal. FMJ rounds are considered standard and sometimes referred to as "ball". Generally these rounds are designed with little to no expansion in mind. Which means that the bullet will maintain its circumference during and after penetrating the target. They are comparatively inexpensive, feed well and give good penetration in most materials.


JSP is "Jacketed Soft Point" and is used to describe rounds that are encased in a metal jacket, again, usually copper alloy called gilding metal, but leave the soft lead core exposed at the tip of the bullet. The soft nose deforms upon striking dense mediums, and these rounds are generally designed to expand rapidly at the nose and mushroom, ensuring that the center of gravity stays in front, and causing the bullet to continue traveling forward through the target. The larger frontal surface area causes more tissue disruption compared to most non-expanding bullets.




JHP is "Jacketed Hollow Point" and is used to describe rounds that are encased in a metal jacket, usually copper alloy called gilding metal, but have a small cavity in the nose along with a round opening in the jacket in the nose. JHP rounds are also designed for expansion but tend to have faster "mushrooming" effects because the hollow point is filled with high-pressure material when the bullet impacts, often peeling back the jacket and making a "mushroom" shaped projectile.




Let's look at the anatomy of a round and what happens when it is fired. Killeen Bishop describes it in her article "Ammunition 101."

"Looking at a cartridge from top to bottom, your first layer is the bullet. That's what leaves the gun towards your target when you pull the trigger (assuming all goes well). The next layer is your powder charge. This is the part that actually is quickly ignited by the next layer of the bullet. The very bottom of your cartridge, usually the round shape at the base, is your primer. Primers can be ignited by striking the outside of that round shape or right on the inside of the round base, depending on whether or not it's rim-fire or center-fire ammo. What happens when you fire a gun is that the firing pin inside the gun hits the rim or center fire. This causes an ignition of the powder inside the casing, which causes the bullet to propel forward towards your target and the casing to expel out the ejection port. This is how the casings end up landing all around, and sometimes even down your shirt. Since the casings have housed the fiery dance between the primer and the powder, they are inevitably hot, thus, you don't want them to land down the front of your shirt and nest. ;) Don't worry ladies. I've even seen some men do the "hot casing line dance", too. It does happen and for the most part you don't have any control over them with the exception of what kind of clothing, hat, and eye protection you wear to inhibit the rogue piece of hot brass."

Here is a great video by NRA Women covering ammuniton