User blog comment:Alockwood1/Jericho Cross Versus John Marston (Undead Nightmare)/@comment-26384220-20150917020821/@comment-4392864-20150917021421

Actually, while this may or may not, change your mind, the Rail Rocket works like a Rocket Launcher - doing massive damage - which is why it's used on structures, like Marks of Evil, which is the structure that controls the undead - destroy one of those, and you kill all the nearby foes.