Metro Last Light

This is really easy to get if your are patient on Mission 13 bandits. This level actually has a merchant that is accessible from start to finish of the level, he is near the camp right at the beginning. So what you want to do is go through the level and kill all the enemies {15-25}, then you can sell all of their weapons back to the merchant, and the weapons they drop are often pretty good pistols that sell for 30-60 military grade rounds. I never counted the exact amount myself, but I believe you can easily get over a 1000 rounds just on this level alone on the easier difficulties. Plus this makes any of the harder difficulties a lot easier since you should have enough military grade rounds to last you pretty much the rest of the game even if you use them frequently.

The following link shows a good way to make it through the level using sleath and also shows the merchant that I am talking about at the very beginning, starting at 53.21.

Its also my recommendation, that you clear out enemies until the area in the middle where you rescue the male hostage, collect the guns and sell them, then move to the next area, clear the enemies until the closed gate, collect the guns and sell them, and finally do the last area past the toxic sludge.

Two last tips, there is a shotgun at the very beginning if you backtrack a little bit, and your weapons shouldn't disappear, so feel free to drop the weapons you want to keep right at the beginning, that way you can grab more guns to sell at one time, although the game always forces you to keep one weapon.