Instructions
Fill your Deadeye meter to at least 50 percent or more. It will come in handy to have this available when you are performing the hunt, which will make the fight go much smoother and also much quicker.
Stock up your ammunition so that you are at max capacity. If you have full ammo you will not have to worry about wasting bullets or running out while you are shooting.
Travel to the gang hideout at Twin Rocks without alerting the men there of your presence. Refer to your map if you need help finding it.
Hide behind a rock and target the man standing on the roof, the man on the giant rock nearest you, and the man on the farther rock all at once with your Deadeye activated and kill them before you shoot any of the others. If you have enough Deadeye, target some of the men on the ground as well.
Kill off the rest of the men just by shooting them normally. There will be a second swarm of men from inside the building. By then you will probably have charged up enough Deadeye to target off several of them, making your job easier. This will give you plenty of experience points (well over 800).
Replay the mission as many times as you need to get the desired amount of experience points. After doing it a few times you will most likely develop a technique for completing it quickly and thoroughly.