>Like, I'm fairly sure I can wuss out with a centerfire round is (the
>firing pin strikes the center of the casing, along the axis, yes?) but
>I'm at a loss as to what a 'rimfire' is

Well, I can take this one on (and you can probably find some handy visual aids to supplement these descriptions on Wikipedia). Rimfire is basically just what it says on the tin: the explosive priming compound is rolled into the rim of the cartridge, rather than being contained in a primer fixed in the center of the cartridge face (as you correctly deduced that centerfire works). The firing pin crushes a point along the rim, setting off the compound, which is directed into the powder charge by the construction of the case.

Nowadays, you hardly ever see rimfire cartridges above .22 caliber (and only rarely below), but they were a fairly common way of doing metallic cartridges in their early days (mid-1800s), up to quite large calibers. They're fairly easy to manufacture, since they have fewer parts than centerfire cartridges, and they have the advantage that if they fail to fire, it's possible (albeit not necessarily easy) to rotate the cartridge a few degrees and try again with a fresh bit of rim. On the other hand, they can't be reloaded, and they offset their, um, hit-again-able-ness by having a higher probability to misfire in the first place.

.22 rimfire, specifically in the form of .22 Long Rifle, has survived into the modern day because it's (relatively) inexpensive, compact enough to be packaged and sold in large quantities without a lot of fuss, and is generally mild and inoffensive to shoot. This makes it both novice-friendly and convenient for experienced shooters who just want to get through a lot of rounds without punishing themselves unduly. It's virtually useless for hunting except on very small game, and although plenty lethal enough to warrant treating with care, you'd have to be pretty confident in your marksmanship to depend on it for self-defense, so it's most often used for target shooting and plinking.

(Plinking, in case anyone doesn't know, is just what it sounds like: target shooting, except instead of formal targets, you're shooting at bottles, tin cans, and various other items of shootable junk.)

To expand a little further, because why not: Modern centerfire cartridges use what's called the Boxer primer system, which means the primer is a separate modular component that's press-fitted into the primer pocket in the center of the face. One may also encounter the earlier Berdan primer, which looks the same in an assembled cartridge but is constructed in such a way that they're much harder to remove and replace once expended. Berdan-primed cartridges are often dismissed as "unreloadable", but the truth is that they're just enough of a hassle to reload, unlike Boxer cartridges, that hobbyists generally don't bother.

There have been a number of other cartridge ignition systems tried over the years, many of them devised in efforts to circumvent patents on centerfire systems and promptly abandoned as soon as those patents were no longer in force - pinfire, teatfire (seriously), and so forth. Ian over at Forgotten Weapons has done a number of pieces on 19th-century guns using different oddball ignition systems.

--G.
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Benjamin D. Hutchins, Co-Founder, Editor-in-Chief, & Forum Mod
Eyrie Productions, Unlimited http://www.eyrie-productions.com/
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