When the mission begins you will find yourself in a jail cell, talk to Port and he will tell you that in order to escape the guard will need to die. Wait until the guard falls against your cell wall and grab him by pressing Y, Soapy will then tell you to kill the guard and you will do so automatically, once he is dead follow Soapys instructions to break out of the cell. Grab your equipment from the guards desk and then follow Port outside. Equip your new bow and head to one of the horses, quietly kill all of the guards and take the horse back to the bridge. Repeat this for two more horses. Once all three horses have been stashed under the bridge, head over to the livery and throw a couple of Whiskey Bombs at the highlighted area by pressing LT , then follow your compass to find some barrels of TNT, kill any guards that are near and take the TNT back to the jail, place it in the highlighted area, stand back and blast Soapy free. Go back under the bridge and hop on a horse, then all you need to do is follow Port back to the rebel hideout, once you get there, the achievement will unlock.