The introduction of the self-contained metallic cartridge made firearms a lot more reliable.
Prior to its introduction, ignition could be an iffy thing. Matchlocks and flintlocks were vulnerable to rain, and while the introduction of the metal percussion-cap improved things, it still wasn’t perfect. The little caps were hard to handle, and there was still the problem of the ignition system being on the outside of the gun and the charge it was supposed to set off being on the inside, which was less than ideal. Combining the cap and the charge in a self-contained cartridge was an obvious winner.
Early revolvers had little difficulty busting caps. A great big spring down in the grip frame would be connected to a substantial pivoting hammer, to which in turn was firmly affixed a nice, sharp firing pin that would pass through a hole in the frame, and crush that little primer with a satisfying BANG! Easy peasy.
A striker is a firing pin that sits in the slide and is surrounded by its own spring. This is more compact, as the whole ignition system fits in the slide.
Obviously, this needed a bit of revision with the advent of the self-loading pistol. Since the whole top half of the gun moved briskly rearward on firing, it wouldn’t very well do to have the firing pin attached to the hammer; you’d need to replace it after every shot, the previous one having snapped off. The most common solution in the early days was to put the firing pin in the slide and just hit the protruding aft end of it briskly with the hammer.
However, instead of a two-piece ignition system, you’ve now doubled your parts count. Enter the striker.
A striker is a firing pin that sits in the slide and is surrounded by its own spring. This is more compact, as the whole ignition system fits in the slide. It does away with the external hammer and makes the gun more snag-proof and reduces the number of parts. Once largely found on inexpensive pocket pistols, striker ignition is found on all manner of autoloaders today. It is not, however without a fault.
Most notably, the use of a smaller spring generally means there is less total energy in the ignition system to deal with a recalcitrant primer. The primers on military ammunition, for example, tend to be harder than on commercial rounds, to make them more resistant to rough handling and repeated chambering. If you use a striker-fired pistol and have found a great deal on military surplus ammo, buy a box or two to try out first and make sure that your pistol likes it before you go ordering three cases of ammunition that may have primers too hard for your gun to reliably set off.
Lastly, be aware that strikers can be more sensitive to dirt and debris than conventional hammer-and-firing-pin setups. Whenever you have your sidearm disassembled for cleaning, ensure that the striker channel is clean and dry and that the striker moves freely in it. During the firing cycle, small metal shavings, powder gunk, and other residue can get through the hole in the breech face and gum up the works, so check for this.
[ Tamara Keel has been shooting guns as a hobby since she was eighteen. She has worked in the firearms business since the early 1990s. Her pastimes include collecting old guns, writing, and being bossed around by house cats. ]