You can look for at least one minigun with ammo, from dead unity guy, and then try to burst better raiders (those with fn fal rifle). Im not sure, how it works this session, but last time, they never shot you first (there was no karma influence on them), so you can easily reach point blank and kill them.
The "medium" ones doesn't attack you until you make first move or talk to them.
Now what would you say to someone who went thru hell in searching for armor blueprint and after finally eating it came to realise that there are HQ fibers in game which are next to ipossible to aquire xD
i know what you mean kinda sucks that you can build a weapon but not the ammo for it. before last patch m60 even needet advanced workbench (i was like WTF?! ). As for the caps i dont get any from my faction and have to get them on my own (solo playing ) but srsly 3k caps is not that hard to get! 30 metal parts 30 wood 120 junk... this resembles 60 spears = 3k caps1hour (well maybe some minutes more due to the fact that junk is now only one piece per pickup) farming and you're ready to go... oh damn did i mention the rep farming for gun runners because you need advancend workbench for the 7.62 ammo?!
According to this it needs normal workbench: http://www.fo2238.fodev.net/wiki/7.62mmSimilarly even advanced gunpowder needs normal workbench!