First off, this is intended for the uninitiated. Those with a great, or even moderate, level of firearms knowledge can skip this without the fear that they've missed the chance to learn something new. I've always found, though, that a little bit of knowledge laid out clearly and simply can help beginners, as well as educate people who otherwise have only a glancing interest. I'll try not to be too geeky, and only lay out the basics.
There are a bunch of different ways to classify firearms, and gun geeks could argue about it all day, I'm sure. I'm going to give you the breakdown that is most useful to beginners, as it will give you a general overview of what is available and some of the terminology. What these categories don't include: old weapons that no one (except history buffs) use anymore (eg. muskets), and weapons that you and I cannot simply walk into our local gun store and buy (eg. machine guns).Handguns
Most knowledgeable gun owners would break this down into two groups: revolvers and semi-automatics (sometimes just called "automatics"). This isn't how I break it down personally, but in the spirit of education I'll do it that way, just for you.Type 1: Revolvers
A revolver is a handgun whose bullets rest in a cylinder that rotates one position with every pull of the trigger. You've probably seen these most often in 1960s and 70s police shows, and as the weapon of choice for battered women in Made for TV Movies. People choose to use revolvers over automatics for a variety of reasons, mostly "tool" related, but sometimes for "fashion" purposes as well. Revolvers are super-reliable. A revolver cannot jam like an automatic (think war movies were someone yells "it's jammed!"). The mechanics are much simpler, and therefore significantly less prone to error or breakage. As tools, revolvers do their jobs time and time again without fail.
From a fashion perspective, some people simply prefer the look of a revolver to the look of an automatic. Some people find them less intimidating, and therefore are more likely to buy one and actually learn to use it. Of course, some people find the look of a revolver more intimidating, so your mileage may vary, just like it was, well, fashion or something.
Revolvers can hold anywhere from four bullets up to ten, depending on the specific type. Revolvers usually do not have a safety, which is a small switch that will prevent a gun from firing unless it is activated. This is not as scary or dangerous as you might think, though. Once you fire a bullet from a revolver, the next bullet does not come in line to be shot until you pull the trigger again, which takes some doing, as the pull of the trigger has to rotate the cylinder. Contrast this with the workflow of the semi-automatic below.Type 2: Semi-Automatics
Semi-automatic pistols (sometimes just called "automatic") are the other half of the handgun population. Pretty much any pistol you see in a modern military or police TV show or movie will be an automatic. Semi-automatics have an advantage over revolvers in that they can hold more bullets (some can hold up to fifteen), and fire them more quickly too. Of course, this comes with the trade off of more complexity. Semi-automatics have more going inside mechanically, and are therefore more prone to failure. Now, a good quality automatic, like the Colt 1911 pictured above, will work flawlessly if proper maintenance is performed.
If your "tool" sense pushes you toward a semi-automatic over a revolver, there is a huge amount of leeway for your fashion sense. Semi-autos range from beautiful pieces of engineering excellence (like, once again, the above picture) to grotesqueries like this.
By the way, when you hear someone say that a round has "jammed", it means that for whatever reason, the gun failed to load a new bullet after the last one has fired, and that round is now stuck. The round will have to be cleared out, possibly by hand, before the gun will be able to fire again.
In contrast to the workflow of revolvers, mentioned above, semi-automatics reload the gun after every shot, making it ready for the next one immediately. That's both why they need a safety, and why they are called automatics. Get it? The gun reloads automatically. As the gun takes care of getting a new bullet ready for you, the trigger pull can be much lighter on an automatic. It doesn't have to spin a relatively heavy cylinder.
One further advantage that semi-autos have is that they can be made incredibly small. The lack of a rotating cylinder means that the gun can be made entirely flat and quite thin. The Kel-Tec P32
is so small that it will easily fit in the pocket of a pair of shorts, or even into a clutch purse. It's amazing how small it is.Rifles
Rifles are long guns that can shoot faster, heavier ammunition a greater distance than handguns, and do it much more accurately. As with handguns, there are two main groups in the Rifle categories, and it has to do with how they are loaded: manually, or automatically. There are a couple of other types (single-shot, lever action) that I won't go into, but they make up only a small portion of the overall modern rifle inventory.Type 3: Bolt-Action
Every time you fire a bolt-action rifles, you have to raise the bolt lever, pull it back, and put in a new bullet (although many bolt-actions will pop a new bullet into place for you, you still have to move the bolt yourself). A person would choose to buy a bolt-action rifle for two main reasons: accuracy and reliability. Due to the fact that each round is loaded by the user, and not mechanically like a semi-automatic, the parts can be machined much more finely, leaving less wiggle room. This makes for a slightly tighter gun, with greater precision. Also, the mechanisms are very simple, and like the revolver, much less prone to error than its automatic counterparts. When it comes to machines, the simpler it is, the harder it is to break and the easier it is to fix.type 4: Semi-Automatic
Not a whole lot of visual difference between this and the bolt-action, eh? You're right. The only thing that's missing is the bolt handle, and there seems to be a bit more visible hardware. Right again. Semi-automatics are just rifles that prepare a new bullet for you immediately after firing. They will fire as quickly as you can pull the trigger. I mentioned above that bolt-action rifles are considered more accurate. That's mostly true, but only in a small, small way. Most modern, good quality semi-automatic rifles will happily go toe-to-toe with their bolt-action counterparts in the accuracy department, so you don't need to worry that your semi-auto is going to be flinging bullets all over the place without your consent.
As with handguns, the same rules apply here. You can shoot more bullets more quickly with a semi-automatic, but you have to do the maintanence, and you run the risk of rounds jamming when the gun attempts to load them.
In this section, my mind is kind of spinning at the compression of so vastly many kinds of rifles into a single category, but I'm going to have to let it stand. I'll just say that semi-automatic rifles run the gamut from simple target shooting and hunting rifles to elaborate paramilitary monstrosities with all sorts of prongs, attachments and doodads sticking out of them.Type 5: Shotguns
Shotguns are long guns, like rifles, but they were designed to shoot a bunch of small pieces of "shot" instead of a single bullet. These little pieces of shot can be smaller than BB's, or as big as 1/3" in diameter. Obviously, the smaller they are, the more you get with each shot.
Shotguns are ideal for two things: hunting and home defense. Due to the fact that the shot scatters a bit when you fire, it is great for bringing down fast moving targets like birds and small game. You don't need to be nearly as good of a shot as you would with a rifle. Using the heavier shot (or even slugs, which are a bullet-like single projectile you can shoot from a shotgun), a hunter can bring down deer or even dangerous, larger animals.
On the home defense front, shotguns are seen by many as the ultimate weapon. They are easy to operate, which is essential as you'll probably be crapping your pants if you ever have to use it for home defense. Likewise, they do not require pinpoint accuracy (think "just point it down the hall and pull the trigger"). Finally, a missed shot with a shotgun will be less likely to go through numerous layers of drywall and studs and into the rooms of the people you are trying to protect.Conclusion
So that's my big five, right? Wrong. Being the practical person that I am, my five useful categories resemble, but are different from, these. I don't personally see the need for a revolver or a bolt-action rifle. I would divide the pistol and rifle categories not by their mechanisms, but by their usefulness. For me, pistols fall into the "practice/play" category, like my Ruger MKII
which is great for cheap target shooting and handgun familiarization; and the "work" category, which would be something like a Kel-Tec P11 or a Makarov whose job would be to destroy and/or kill things if the need should ever arise. Same for the rifles: "practice/play" in the form of .22 (small, fairly low-powered) rifles which are once again cheap enough to shoot day-in-day-out without financial pain and are good for things like killing groundhogs; and "work" rifles like a semi-automatic .308 for, once again, actually destroying/killing things should that ever be the task at hand. Shotguns are still shotguns to me, and they make me smile.
Hopefully, this was little enough like a textbook that you were able to get through it without falling asleep. I'm also hoping you learned something, too.Note to gun aficionados who have read this far: this post is intended as a primer for complete firearms noobs. I realize that many of things said here are simplifications, and that in many cases exceptions to my statements have not been mentioned. If you want to nit-pick, there are tons of gun forums on the Internet where people do that very thing every day. I invite you to go pick on someone somewhere else. If, however, you've noticed something here that is factually incorrect and could mess up the knowledge base of someone just getting started, then by all means, please let me know. Thanks - Roland