A primer is basically a little metal cup filled with priming compound, which is pressure-sensitive and ignitable; you hit it and it burns. The primer is the spark plug of the cartridge, it provides fire to ignite a flammable material, in this case gunpowder. There are two primer types in common use today to transfer impact pressure from firing pin to priming compound: the Berdan and Boxer systems, each named after its inventor.
The Berdan system was developed by an American ordnance officer, Hiram Berdan. It consists of an “anvil,” a post extending from the center of the primer pocket up into the primer cup. When firing pin hits primer, it mashes priming compound between cup and anvil, causing it to ignite. The resulting flame flows into the interior of the cartridge case through two small flash holes, located somewhat offset from center, thus igniting the gunpowder.
About the same time Berdan was developing his system, a British ordnance officer named Edward Boxer invented his own, using the same basic idea (firing pin mashes priming compound between cup and anvil) but in a different fashion. In the Boxer system, the anvil is not part of the cartridge case, it’s part of the primer. Because the center-floor of the primer pocket was not taken up with an anvil, Boxer was able to place there instead a single, large, centrally located flash hole.
Ironically, the Boxer system, developed by a Brit, was adopted wholesale by American ammunition companies; the Berdan system, developed by an American, was adopted in Britain and pretty much everywhere else in the world.
Once we’ve fired a cartridge, the spark plug is dead, the priming compound is gone, all burned-up. In order to handload that cartridge and turn it back into fireable ammunition, we need to replace the primer. Unfortunately, the centrally located anvil and double offset flash holes of the Berdan system make reloading cases using Berdan primers, while not impossible, extremely difficult.
Now, famed shooter and handloader Ross Seyfried, when he wanted to handload an obsolete, big bore English rifle cartridge never produced in a Boxer-primed version, did manage to get his hands on some Berdan primers (not commonly available as reloading components, by the way) and jerryrig a little double-pronged hand tool to decap Berdan primers. However even Ross commented that making the tool, and actually using it, were both painstaking, time-consuming undertakings suitable only for turning out a small quantity of ammunition, and that only if there were literally no other choice.
For all practical purposes, Berdan-primed cases are non-reloadable. The only time we commonly see Berdan primers in North America, they’re used in Blazer ammo specifically to prevent people from reloading the aluminum cases.
With the Boxer system by contrast, and its single, large, centrally located flash hole, it’s a simple matter to run a rod, called a decapping pin, down into the case, through the flash hole, and punch out the primer, emptying the primer pocket and readying it for a new primer. The dead spark plug can be replaced.
In recent decades, factories in some other countries have begun producing Boxer-primed ammo. But Americans got a huge jump on the process. The fact that Boxer primers are easily removable/replaceable, and North American ammunition companies went to the Boxer system early-on, made the United States the incubator for handloading technology, and it’s one thing allowing, for instance, your Dillon reloading machine to exist and work. Handloaders owe a huge debt of gratitude to Edward Boxer.
