Found this gem of a game.
It's a mix of Stalker and DayZ, but handles like Vietcong.
https://www.youtube.com/watch?v=O3wxhozLVLIOnly iron-sights aiming (you get really good fire fights, bullets flying all over the place).
You keep the weapons you find, if you survive, and if you have space for them in your stash. Every bit of most guns is modular. You can buy and find parts.