Heres a tip to getting the best dmg weapon very early in the game called Derek's pistol, it's a unique pistol that can be obtained by ddefeating derek in the no gas slaver event here are the items you need to fight derek and win.
15 canned tuna
Scrap helmet and armor
And your dog companion
The dog is optional but it's better if you do it because the dmg is worth it, to beat derek you need to equip both armor when you buy them it's gonna take some p*say licking or if your brave enough, get fucked for 10 grams or 5 grams for a bj and a cunn you can find the dog in the forest it's best if you had the armor by now since your fighting 3 wolfs instead of 1 since their hp is 3 times larger they also deal more dmg than a regular one, you also don't need to do the no gas slaver event early it's a side quest so prep before you start it when frank asks you to get the weapon crate if you have 7 charisma you can haggle for the original price which was 100 grams but was raised to 200 grams after you get the weapon crate there's no time limit so grind as much as you can but to be safe get 20 canned tuna, once you give frank the guns you need to join the defence if you don't you'll miss out on a companion and a safe house as well as Derek's pistol once the defense starts your instantly going into a fight with Derek no use trying to let him go he's a slaver so he needs to die start the battle and don't use any weapons ever you'll have a better chance of beating him to death than using the crappy guns johnny sells make sure to check your hp after each hit heal 60 or below hp 2 times with the cans keep doing this and you get Derek's pistol it's your choice on what to do with him I just killed him in my playthrough.
After events: after the defence if you joined Frank will say that people were hurt but not killed if you eliminate derek he gives you a reward as well as the safe house I mentioned it has 3 upgrades and you can buy them from your next companion if you do it right.
When you beat derek you grab his pistol and some bullets the dmg for Derek's pistol is 45-50 it's not the highest dmg weapon the Duelist is the highest dmg weapon but that's for later in the game with this pistol you should be able to beat very dangerous enemy's but you still need armor and more healing items if your hoping to survive them.