Elite-ranked weapons are the highest tier and best weapons in the game. However, you can further upgrade them and increase their damage by 5% by spending a fixed amount of resources, including ethanol and hard-to-find ones like Carbon Fiber. These are permanent upgrades which will even make your weapon of choice a whole lot deadlier. My personal recommendation would be the bow, LMG or grenade launcher or the sniper rifle. Both are perfect for most combat scenarios.
Once the workbench reaches LV3, you can infinitely upgrade your weapons using replenish-able resources like Ethanol. This means you’ll have to scavenge 3-star outposts over and over again. You can do this operation on any workbench. Once you're able to one-shot or melt Enforcers, it will be a waste of time and materials to increase the damage of your weapons any further.
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