I know in general how a gun works. You pull the trigger, and a bullet comes out the other end. Right?I even know how a cartridge works. The bullet is at the top, and there's a charge of explosive powder below it. The powder goes boom, and the rapidly expanding gases push the bullet out the front at very high speeds, eventually transmitting a great deal of kinetic energy to something.
But there's a bit there in the middle that I didn't quite understand. In an olde-y time-y gun, there'd be a spark or fire or something that would light the powder, starting the explosion. But I don't think that's how it works these days. I've heard tell of something called a "firing pin," for instance. To the Research-mobile! Nananananana...
The missing piece, historically, is a little separate doohickey called the percussion cap. This was a small container, open at one end, containing a small amount of a substance that explodes when triggered by a physical impact, rather than a flame or electrical charge (like black powder or C4, respectively). When the trigger on a gun was pulled, a spring-loaded hammer would strike the percussion cap, causing the contents to burst into flame, which would then travel into the main propellant, causing the bullet in turn to go whoosh.
These days, the percussion cap is integrated into the cartridge, which contains not just the bullet and the propellant (as I thought) but also a separate charge of primer, which is the impact-sensitive stuff. The hammer or firing pin strikes the primer part of the cartridge, causing an internal chain reaction, making everything go bang.
So that's that sorted. Heck, if I still feel shooty tomorrow, I may try to figure out how other bits of a gun work. That whole automatic reload thing is kind of mysterious, too...
