Back in Armadillo, you’ll find Irish being roughed up by two men very displeased with Irish’s attitude. French and Welsh approach John with the intent to do bodily harm, so you’ll have to take them out before you get a chance to speak with Irish. Jumping to Dead Eye and shooting both men is the quickest and easiest way to get the mission moving along.
Once you’ve saved Irish, he informs you of a place where you can get a gatling gun to help in the assault on Fort Mercer. Grab your horse and follow Irish to Lake Don Julio. There’s a small shack by the lack where Irish insists you’ll be able to find the firepower you’ve been looking for. Irish fails to mention the half-dozen bandits guarding the shack.
There’s plenty of cover to hide behind while you shoot it out with the bandits by the lake. Once you’ve eliminated everyone outside, make your way to the shack. Be prepared, as there’s one more bandit inside who tries to jump you when you get to the shack’s front door. Unfortunately, after searching the shack, it appears Irish has misled Marston. With little to show for the effort, it’s time to track Irish down for some answers.
You’ll find Irish passed out behind the same train station where you and Seth found Moses. A little worse for the wear, Irish isn’t exactly forthcoming with help or new information. Irish may have a line on another weapon though, and leads John to Gaptooth Breach, where some treasure hunters are holding onto another gatling gun.
After following Irish to the mine, you’re met by two riders guarding the encampment. Use Dead Eye to take them both out before either has a chance to draw their weapon, and proceed into the camp. There’s a small handful of other treasure hunters outside who will make it rather challenging for you to get inside the mine, but by sticking to cover and taking them all out, you’ll be one step closer to that machine gun.
When the last treasure hunter falls outside, it’s time to head into the mineshaft. There are plenty more treasure hunters holed up inside, but you can take them on one-by-one for the most part. There’s even strategically placed dynamite crates throughout the mine, which make quick work of any enemies when you shoot them. As you proceed deeper into the mine, you’ll find a central area guarded by small wave of hunters. Take them all out, and check the mine cart to find the machine gun.
You’ll have to push the mine cart to the other side of the mine to get the gun to the rope elevator. Irish will pulls you and the gun up, but there’s still the little matter of escaping one last batch of treasure hunters. Merely hop onto the back of the mine cart, using it for cover, and ride along the tracks shooting any hunter that comes into your sights.
Once you reach the end of the tracks, Irish loads the gun into the back of a wagon, and heads off. You’ll be catching up with him again at Thieves’ Landing.