If you want a placeholder until you work out interactions, just make ammo with a fairly high contact area but much lower penetration. Say it "showers them in a spray of pellets" or something. It won't hit them multiple times, but it'll do more or less what you would expect a shotgun to in terms of damage. Widespread damage, especially to soft fleshy bits, but less armor penetration/bone shattering/killing things 10 times your size. Because of the low penetration, it'll be especially effective against smaller animals and still effective against those as large or larger than Dwarves. If creatures are too large, it won't penetrate enough to do serious damage, because buckshot is meant for killing bucks. Not dragons. It's good enough until you work out the rest.
The AI wielding these weapons aren't going to throw them. They'll level up throwing when they attack in melee combat. There's no way to make throwable weapons outside of adventurer mode since every ranged weapon needs both a launcher and ammo.
Adding onto this: while you technically can't make a thrown weapon, you can make it
look and
act like it's a thrown weapon. Basically, you have a melee weapon that acts as a launcher, but you disguise that fact. So you might have:
[ITEM_WEAPON:ITEM_WEAPON_SWORD_THROWING]
[NAME:short sword:short swords]
[SIZE:300]
[SKILL:THROWING]
[RANGED:?:?] (Whatever you want to throw will be your ammo)
[SHOOT_FORCE:1000]
[SHOOT_MAXVEL:1000]
[TWO_HANDED:37500]
[MINIMUM_SIZE:32500]
[MATERIAL_SIZE:3]
[ATTACK:EDGE:20000:4000:slash:slashes:NO_SUB:1250]
[ATTACK:EDGE:50:2000:stab:stabs:NO_SUB:1000]
[ATTACK:BLUNT:20000:4000:slap:slaps:flat:1250]
[ATTACK:BLUNT:100:1000:strike:strikes:pommel:1000]
As an example:
[ITEM_AMMO:ITEM_AMMO_JAVELINS]
[NAME:javelin:javelins]
[CLASS:THROWN]
[SIZE:400]
[ATTACK:EDGE:20:5000:impale:impales:NO_SUB:1000]
In the inventory, it will appear as though they have a short sword (which works just as well in combat as normal), and independent of that, javelins. They will throw the javelins and then proceed to fuck shit up with their sword instead of whacking away with a crossbow or something. It's not perfect. If they lose the sword, they can't throw the javelins. Of course, if they lose the sword, they will often still use the ammunition as a melee weapon from what I've seen, which works pretty well. It's about as good as you're going to get, and other than that kink, it works out perfectly. It's also very easy to do.
If you have a bunch of launchers disguised as normal weapons, you might want to add "(t)" or "(throwing)" or something at the end of them so they're easier to distinguish. So your short swords would appear as "short swords (t)" or "short swords (throwing)", so you don't mix up your actual and fake short swords. If you make all throwing weapons in the class "THROWN", then any launcher-disguised-as-weapon will be capable of throwing any throwing weapon. So if you wield the short sword, you could use everything from throwing axes to knives to javelins to giant rocks. Whatever you want.