What Are Reloading Primers, and How Do They Work

Modern cartridges are primarily composed of five major parts: the projectile, the case, the rim, the propellant, and the primer. Some shooters will want to reload their own ammunition out of intact cases for practical or recreational reasons. Of those that do reload ammo, the ins and outs of propellant and projectile selection are often the main focus, rather than the primer.

However, home reloaders will often overlook primer selection at their peril, as the choice of primer can have a major impact on the reliability of their ammo and even influence the types of ammo they will prefer. And while most shooters may just buy ammo online and never feel a desire to learn how to reload their own ammo, understanding what reloading primers are and how they work can be important for getting a better appreciation for the engineering and craftsmanship that goes into firearms.
What Are Primers, and What Are They For?

A primer is a chemical or a device designed to set off a secondary charge. In the case of most types of ammunition, primers are a small, shock-sensitive explosive that sets off the propellant powder after it’s struck by a firing pin. While there are some notable exceptions to this, such as in the case of electrically fired ammunition, the vast majority of ammunition you’re likely to find is going to use some kind of chemical primer.

In early black powder firearms, the primer was usually the same chemical as the propellant, albeit with finer grains to reduce the chance of misfires. In contrast, the propellant powder typically used in the majority of modern ammunition designs is different from the one used as a propellant charge.

Whatever the design, the primary advantage of using separate primers and secondary propellant charges rather than just one chemical is that it can help improve both the safety and reliability of the ammunition. Black powder is extremely volatile and can easily explode when subjected to shock or heat. This meant early black powder firearms also had a tendency to go off unintentionally. Ironically, black powder also had problems with ignition reliability, particularly when exposed to humidity. This meant that they often fired when one didn’t want them to—and didn’t fire when the user’s life depended on it.

The design of modern self-contained ammunition with a separate primer was partially a response to these problems. Propellant charges are deliberately designed so that it takes significantly more force to set them off, which is why a separate primer is needed. To further improve safety, primers are designed to be set off only by the deliberate application of mechanical force, usually by a firing pin.

Types of Reloading Primers

Technically speaking, any conventional ammunition type with a case and a chemical primer can be reloaded. Both centerfire and rimfire cartridges can be reloaded. However, when manual reloading is discussed, it most often involves centerfire ammunition, as this is the most common type of ammo for rifle and handgun cartridges.

Conventional centerfire cartridges typically use one of two types of primers, Boxer and Berdan. Both primer designs were patented by their inventors in their home countries in 1866. Without getting too bogged down in technical minutiae, Boxer primers have more parts and are more complex to manufacture compared to Berdan. However, Boxer primers are vastly simpler to reload. Modern automation has made the slightly added complexity of Boxer primer manufacture a non-issue, and most centerfire ammo today uses Boxer primers.

While rimfire ammo can be reloaded, it’s typically less popular to do so as the process can be somewhat fiddly. Unlike with centerfire ammo where the old primer with the striker pin dent is normally discarded, rimfire ammo has a different design, which means a shooter using reloads will have to either just reuse the case with the dents or find a way to remove the dent, which is rarely worthwhile. Unfortunately, the dents in the case from the firing pin can cause issues with the reliability of rimfire ammo. The extremely low cost of popular rimfire ammo like .22 Long Rifle also reduces the incentive to reload this type of ammo and make reliable reloading solutions more widely available.

Why Else Do Primers Matter?

Whether you plan on going into reloading as a way to save money, make wildcat rounds, or have some kind of obscure ammo, you need to make sure that you purchase the correct tools and primers for the job.
This is the case even if you’re not into vintage or unusual firearms. For example, AK-pattern rifles in 7.62×39mm are extremely popular. However, the most common type of ammunition available for them in the USA is the Russian and former Soviet Bloc steel-cased type, which overwhelmingly use Berdan primers. This is because this ammo was designed to reduce the cost of manufacture and didn’t have home reloading in mind. The combination of steel case and Berdan primers are a veritable nightmare for novice reloaders. There is, however, brass-cased 7.62×39mm with Boxer primers as well.

That is only one instance where knowing the type of primer used matters. If you plan to shoot regularly or collect unusual firearms, you will undoubtedly need to consider learning to make reloads. And when you do, you will certainly run into different scenarios where the primer choice can be a critical factor.


If you do plan on investing in the tools and knowledge needed to get into ammunition reloading, learning about the different primer types is just one of the basic things you’ll need to do. Generally speaking, however, knowing more about the ammo available for your favorite firearms—and the primers they use—can go a long way into helping you make better, more informed choices.

All opinions expressed on USDR are those of the author and not necessarily those of US Daily Review.