Most feasible homemade firearms for castaways?

For a big group of competent people on a tropical or semitropical island, what would be the most feasible type of firearms they could produce on their own with quite basic tools and equipment, provided that they already have the ingredients to make gunpowder?

My thoughts went to flintlock firearms since they seem relatively simple and feasible to make, but a friend of mine wondered why they could not just make percussion firearms instead. I had a look at those and while they do seem superior in every way they also seem a degree more complex. Perhaps too much.

Any historical gun expert want to chime in?

First off, you're forgetting matchlocks and handcannons. You don't need a flint and steel, just get a burning ember on a stick and push it through the touch hole.

Second, firearms need a certain level of structural integrity or they'll explode in your hands. It's easier to make a crossbow.

Third, percussion caps require mercury fulminate or a similar impact sensitive explosive. This requires some fairly advanced chemistry.

Edited by Belisaurius on Jun 25th 2020 at 9:47:41 AM

What do they need a firearm for?

To make firearms, you need a metallurgy industry. Probably won't have that as castaways on an island.

You can make a cannon out of duct tape so...

You probably won't have rolls of duct tape as castaways on an island, either. Unless it's one of those exotic islands that features a fully stocked and recently abandoned hardware or office supply store.

Edited by Fighteer on Jun 25th 2020 at 10:07:40 AM

The castaways were shipwrecked aboard a freighter carrying a boatload of duct tape.

I'd go with a crossbow as well. You can make the prod out of a strip of hardwood, or several strips of softwoods lashed together, as in some historical Chinese designs. The trigger mechanism can take several different forms.◊ You'll probably need some metalworking for the parts, but it's still a lot simpler than a whole gun barrel, so you could probably cast them by melting down aluminium or tin (pewter) into a simple sand mould - and if it doesn't work, then hey, at least it won't explode in your face. The string can be twisted together from just about any plant fibre you can find. The bolts' heads can be made from any scrap metal you scrounge up, and the fletching from plastic or rubber sheets. And if the draw weight ends up heavier than you're comfortable with, then you can fashion a mechanical aid like a windlass◊ or a goat's foot lever.◊

I'll add that black powder by itself burns slowly and haphazardly on account of irregular grain sizes. To make it combust efficiently enough to be a firearm propellant, you'd need to "corn" it by wetting it (careful that you don't end up contaminating it with dirty/saline water), pressing it into a dense "cake", letting it dry and then carefully chipping it into small, regular grains. That's not counting the painstaking work of forging iron into the barrel, chamber and trigger mechanism (at a way higher temperature than casting aluminium or tin). A crossbow would only need a small fraction of the metalworking required for a gun. And less woodworking, too, when you remember the sheer amount of wood you'd need to charcoal and burn to get iron up to forging temperature.

Mythbusters also made a cannon out of a log.

Though yea, the limiting factor will be iron working. Castaways on an island probably won't have much of an industry.

One possibility that occurs to me is that, as castaways, they may have access to wreckage or cargo that could stand in for working the metal themselves.

For example, perhaps they had been travelling a ship carrying amongst its cargo appropriate steel tubing, open at only one end, thus potentially allowing for a simple front-loaded firearm.

(I do suspect that a crossbow would be a safer and more efficient use of their likely resources, however.)

Yeah, ready-made infrastructure and materials would change the cost-benefit calculus quite significantly. Basically, in 16th century-ish Europe, steelworking technology became advanced enough that you could start producing gun barrels en masse and plate armour of various grades... but you still couldn't make steel crossbow prods that could hold enough elastic potential energy to launch a bolt through said armour, while the chemical energy of a musket's powder load was capable enough of doing so.^note There were 16th-17th century exemplars of "bulletproofed" breastplates and helmets, but these were usually several times thicker and more expensive than regular high-end ones. The weight made it impossible to apply that level of protection to the limbs. And of course, no amount of armour is going to save you from a cannonball. Or heatstroke.

A crossbow has a far lower tech "floor" to make: with some wood, fibres and a comparatively small amount of metal, you can put together a reasonably reliable one that could put a bolt through small prey animals. A crude, barely-functional musket is going to need way more metal, way more fuel,^note Of course, if you have ready-made barrels in place, then you could simply drill a touchhole near one end and kludge together some external mechanism to turn it into a matchlock - no hot-forging needed. more extensive metalworking facilities and a steady supply of gunpowder; in fact, at this stage, your community would probably be well beyond the "survival" stage and had established themselves quite comfortably on the island. Once you have those things, though, you'd be able to mass-produce cast bullets more easily than crossbow bolts, and your muskets could potentially shoot farther and bring down tougher targets than any crossbow could. Above all else, firearms benefit from the economies of scale.

I'd still recommend the crossbow for starters, though.