A Short History Of Primer Initiators

A primer is basically a little metal cup filled with priming compound, a material that’s pressure-sensitive and ignitable, in other words, you hit it and it burns. The primer really is the spark plug of a cartridge, it provides fire to ignite a flammable material, in this case gunpowder. It would serve us as handloaders to understand something of the history of these fascinating little devices, and how they work, because they’re one huge thing making handloading possible.

PRIMING COMPOUND

Priming compound is a complex blend of chemicals designed to accomplish different things, but for purposes of this discussion we’re interested only in what makes the compound pressure-sensitive and ignitable, which is called the initiator. The history of primers over the centuries really is mostly a story of changes to the initiator.

The earliest primers, going back to muzzleloading days, used mercury fulminate as an initiator. This actually worked really well in such guns, because it was stable and reliable. The problem came with the development of brass cartridge casings: mercury residue from the fired primer would attack the brass, in short order making it extremely brittle thus unsuitable for reloading.

Eventually we got around that by developing primers using potassium chlorate instead of mercury fulminate as the initiator. Unfortunately, we exchanged one problem for another. While potassium chlorate residue does not attack brass, it attacks steel because the residue contains chemicals similar to common table salt. Thus, the bore, and parts near it, as well, would begin to corrode very shortly after being fired with potassium chlorate primers, unless they were cleaned immediately with a solution of hot, soapy water. For this reason, potassium chlorate primers are called corrosive.

In the late 1920s came primers using lead styphnate as the initiator. This is what’s still used in the vast majority of primers to this day, because it solved all the problems. Lead styphnate residue does not weaken brass, nor does it corrode steel. Therefore, lead styphnate primers are called non-corrosive. The idea that a shooter must immediately clean their gun, especially the bore, immediately after every shooting session in order to avoid damage is a holdover from pre-lead styphnate primer days. I’m not saying you should never clean your gun, just saying the idea you must clean it immediately after firing or it will begin to disintegrate is obsolete information. Lead styphnate primers got us past that.

Though commercially sold ammunition went to the lead styphnate system en masse shortly after its development, the American military stayed with potassium chlorate until the 1950s. Such ammunition can still be found on the surplus market even today. Thus, when buying cheap military surplus ammunition, it’s very important to ascertain whether it’s loaded with corrosive or non-corrosive primers.

In the early 1990s, due to concerns over airborne lead when firing lead styphnate primers on poorly ventilated indoor ranges, primers were developed that are lead-free.