Name of recent western movie with a mutual kill scene?

I need to find a mutual kill scene from a recent western movie (last ten years or so).

It involved a walk-thru where a character (could be a woman) moves through a rough and tumble wild west camp. At one point two prospecting brothers(?) argue, whip out their guns and simultaneously pull the trigger. Each falling to the ground at the same time. The scene was enacted in such a way that we know these two fought all the time, were used to pulling guns on each other except this one time they both die as a result.

The character walks past as if nothing happened.

Can anyone identify this move? I need to show this scene to a friend who doesn't believe me.

Thank you.

Maybe In a Valley of Violence or Brimstone.

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I saw Brimstone. It was torture porn. Won't put put myself through all that again.
Will someone tell me what time frame the mutual kill event happens so I can just jump to it?

If you want the answer, I think you'll need to go through the retched movie again.

I don't know why anyone would do what you've said you won't do.

I'm quite sure there's no such mutual kill scene in Brimstone (seen it twice and really like it, btw).

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It might be the end of Sweetwater, with January Jones as the female character. The two guys killing each other are not brothers but I think it could still be it.