Speak to Molly at the camp to begin this mission, Uncle has a lead on a wagon to rob and wants Arthur and some of the other members to help him take it. Mount up and follow Uncle to the marker to wait for the wagon to approach, helping Charles loot the chest in the back when the job goes wrong.
You’ll need to escape the enemies by galloping as fast as possible, taking out any of them with a Dead Eye headshot if they get too close. You need to maintain 80% accuracy in this mission so only go for the shot if you’ll land it. Eventually you’ll come to a stop at a barn and rest for the night.
Guards will approach the barn during the dead of the night, use the left stick to keep an eye on him but stay hidden until Bill blows your cover. You’ll have to hold off all the guards at this point who attack from all sides, use Dead Eye as much as possible (using Chewing Tobacco and Snake Oil to replenish if possible) and aim for headshots. You’ll be attacked from every side so keep an eye on the radar and alternate your cover around all sides of the barn. Eventually the barn will go up in flames and you’ll need to make your escape, follow Bill out the back and into the woods.
Get into cover with Uncle as more guards approach, for the Gold Medal you’ll have to take them out silently so let them pass and then approach from behind to perform a Stealth Kill. Uncle will need help with his Takedown so quickly rush to his aid before running over to help Bill and Charles. Once again stick to cover in this final shootout and try to score the last remaining headshots you may need. There’s a lot of guards to dispatch in this mission so try to keep missed shots to a minimum to maintain that 80% accuracy.