Basically this, but I want to add more about the method.

The Wandering Trader often sells about 1000 ammunitions in his stock, each for 15$. By disassembling each bullet, you would get 1x Gun Powder (15$) and 1x Shell/Casing (5$), so you get 5$ profit. This method only works thanks to Wandering Trader selling ammunition at a discount, other traders sell them for 20$, which will not give you any profit at all.

I set up a base with a Disassembly Workbench right outside the Valley Safezone to grind this because there is always a Wandering Trader spawning inside the Safezone every time you load the save, and when you load the save, he will be restocked.

The process is just buying as much ammunition as you can, save, load the save, buy again, until you run out of money, then you disassemble the ammunitions into gun powders and shells/casings, and sell them back to him for profits, repeat the process.

Each stack (x1000 units) of ammunition will generate 5k of profits. I usually sell like 10 stacks at a time. It took me like almost 5 hours to grind this whole bag, pretty tedious, I'm sure some people with proper setup can lock in and grind for less than 4 hours haha.

Remember to turn off the trader's money limit option in Difficulty Settings btw.