In this next two-part series of articles, we wanted to take an in depth look at primers and how they affect your load. The primer ignites the main powder charge in the cartridge case. Without a good primer, nothing happens when a gun's firing pin falls.
Types of Primers
All ammunition commercially loaded in the U.S., as well as reloaded ammunition, uses the self-contained "Boxer" type primer, developed by Edward Boxer. This little device has a cup, which holds the priming compound, and an anvil. The anvil rests lightly on the priming pellet, which is crushed between the dent made by the impact of the firing pin and the anvil to initiate ignition.
European cartridges have traditionally used primers of the "Berdan" type, developed by Hiram Berdan, which lack the anvil of a Boxer primer. In a cartridge designed for a Berdan primer the anvil is built into the primer pocket of the case, rather than the primer. These cases cannot be de-capped and reloaded by standard reloading tools. I understand that, as reloading catches on with European shooters, an increasing number of European cartridges are being factory loaded with Boxer primers.
It is a rather interesting quirk of history that Edward Boxer was a British ordinance officer, yet his primer design was adopted in the U.S. Hiram Berdan was an American ordinance officer, yet his primer design was adopted in Europe, as well as most of the rest of the world.
What is a Primer?
The priming compound itself is an explosive intended to be detonated by percussion. (It can also be detonated by heat or flame.) There is typically less than one grain of priming compound in even the hottest primers. Nevertheless, primers must be handled and stored carefully. They are, after all, designed to start a fire. Store primers in the proverbial cool, dry place away from other flammables. High humidity degrades primers more than high temperature. According to CCI/Speer, properly stored primers will remain viable for decades.
Keep different types of primers separated so that they cannot be confused. Always store primers in their original packaging, which is designed for safety. Never store primers in bulk, such as in a can or jar. In many jurisdictions, it is illegal to store more than 10,000 primers in a private home.
The standard primer sizes of metallic centerfire (rifle and pistol) cartridges are small (. 175" diameter) and large ( .210" diameter). The standard primer types are pistol, pistol magnum, rifle, and rifle magnum.
Rifle primers use tougher cups than pistol primers because the firing pin blow of rifles is usually harder than the firing pin blow of pistols. Rifle primers also contain more priming compound than pistol primers, since rifle cartridges typically contain more powder than pistol cartridges.
Magnum primers are "hotter" than standard primers. CCI/Speer typically recommends that magnum primers be used with ball (or spherical) powders, when loading magnum or other large capacity cases, and when it is anticipated that the cartridges will be used at temperatures below 20 degrees F. Ball powders are generally harder to ignite than flake and extruded powders and magnum primers are often called for, even in non-magnum rifle and pistol cartridges. Let your reloading manual be your guide to primer selection.
In part two of our series on primers, we will look at how the primer affects your load and how you can experiment to find the best for your reloading needs.