I'm certain I've found this one a few times. The main character is a female undead gunslinger. I forget whether she explicitly goes through situations where she would have died, or it's in her backstory, but I want to say that she's got some sort of facial injury or marking related to her undeath. I want to say that someone tried to hang her? She's in the pursuit of a mad scientist. I think it's eventually (or maybe initially) revealed that they were once lovers, and that she might have worked for him. I think he's trying to locate some secret of immortality. Other than that, my memories are sparse. I remember one episode involved her addressing a train robbery where the focus of the robbery is what seems to be a telescope. Later, said "telescope" shows up in a later episode involving a crystal city and something powerful buried below it, where it's revealed that it's actually some sort of ray gun. In another episode, the gunslinger rides through a town afflicted with a plague, with there being some plot point of the last building still open.
I know it's not Back. The art style is more colorful and realistic, and the plot is decidedly less silly. I think I read it in the last 4-5 years (since 2014 or so) and it was not completed at that time. The tone was definitely greyscale with the indication being that neither character was really evil, just very driven.