revanbh: Your safest bet is to buy bullets schematic early on and invest single point in Explosives. That way you'll be able to make your own ammo rather easy, since it requires charcoal, which can be found in every rubbish bin, and saltpaper, which is also not hard to come buy. You get about twenty bullets every time you combine them.
Buying ammo for your guns isn't really economical.
I agree. But making ammo is frustratingly time-consuming as well.
Here's what you have to do, once you've bought and learned the Bullets schematic:
1) Visit every rubbish bin in Tarant (or whatever town you're in) to scrounge up as much charcoal as you can.
2) Visit the general store, the inventor, the junk dealer and/or the herbalist, and buy out their saltpeter for the day.
3) Combine the items to make bullets.
4) You won't have enough (you never have enough) so walk away from everyone,* advance the clock by one full day, and repeat step 1 above.
Basically, being a gunfighter means grinding for bullets. Not cool, man; not cool.
*Anything within one full screen of where you are when you "sleep" won't reset or restock their contents/wares the next day. This is a minor annoyance for garbage cans, but absolutely critical for shopkeepers.