Choosing a weapon for your character can be as easy or as hard as you make it. You can just pick whatever random thing comes to mind, if you like, and the story very may well flow in perfect equanimity. It remains, however, a missed opportunity, if you don’t take the time to choose a weapon that adds something to the story with its very presence, is almost a character unto itself.
Using weapon choice effectively in a story is about two things. The first is choosing something that is a practical fit, that will serve all the purposes you need it to and allow the story to flow in the way and in the setting you envision. The second is choosing something that is an artistic fit; something that matches your character’s personality; that fits in with the tone of the story; that, in short, makes a statement about what your story has to offer.
Before you get started, ask yourself what you need your weapon to do in the plot. Firstly, do you need a hand-to-hand weapon, or something at range? If you choose the former, you’ve got to find a way for your character to be standing beside everyone they are going to fight for the rest of the book – this is both a challenge and an opportunity. What skill level do you plan to give your character? Some weapons are easier than others – a simple tazer is as point-and-click as it gets, while a katana or Barrett .50 will punish the unprepared user. If it’s a difficult weapon, you’ll have to write a character who had the time to practice with it, or else gets their skill some other way.
Different weapons carry different emotional hooks and weights. A complex edged weapon like a chakram is worlds away from a sturdy club; an army-issue M9 says something entirely different than a customized SPAZ shotgun with incendiary rounds.
In the ancient genres, edged weapons can be a symbol of civilization – the manufacturing prowess necessary to create something like a xyphos is remarkable, and while it’s not historically valid to say that complex metalworking is a civilized man’s pursuit, it does give that impression to the average reader. The time involved in creating the more complex edged weapons is remarkable – the cost is, thus, considerable. If your character carries a chun qiu dao, it cost someone a great deal.
In modern genres, the degree of quality a weapon shows often hints at the person’s place in the world. Someone with an AK-47 probably didn’t just come in with SEAL Team Six. Somebody carrying an M4 is likely not just any old gun nut. That guy drawing his 1911 probably isn’t a beat cop.
The origination of a weapon can tell a story, as well. A character that carries a Micro-Uzi is carrying a piece of Israel – maybe they know that, and that’s why they do it, or maybe they don’t and that’s the irony. Maybe they don’t care as long as it works. In any of these cases, you’ve given yourself a chance at characterization that you wouldn’t have had if you’d just given them any old thing.
Just as importantly, a weapon should fit your character’s personality. Yes, anyone can pick up a meat cleaver and start going to town on folks, but is the person who does so likely to be a warrior monk? An elephant gun will shoot for anyone big enough to hold it up and pull the trigger (with admittedly differing results) but it’s very clearly the sort of gun a specific sort of person is going to be carrying around with them. Does your beautiful, modern-day princess who’s fed up of everyone’s shit have a Glock 9 in a thigh holster? You bet your rising blood pressure she does. Does your Army Ranger on a quest to find his lover’s kidnapper need a KA-BAR fighting knife? If he doesn’t, return him for a different, better one. Does your Roman Legionary deserter have a giant trident and net? Actually, probably not, but he might, and if he does, then you have a particularly cool one.
Every weapon has something to say, a role to play, a set of strengths and weaknesses, a look, a sound, a feel, a soul, and leaving all that up to chance as you pick out the first thing on the proverbial rack is just leaving cash on the table.