Continuity mistake: Frank was supposedly a small child during the massacre in 1857, and the show is set in 1884, meaning only 27 years had passed. And yet he was a much older man. Also, he meets Roy when he's 15, which is at least 10+ years before the show is set, meaning it's only 17ish years after the massacre, which would make Frank early 20s when they meet, and yet he's old, gray, and balding. The timeline makes no sense. They should have either set it later or not made him a victim in the massacre.
Shot the Head off a Snake - S1-E5
Factual error: Frank Griffin makes a reference to Burma Shave in the 1880s. Burma Shave didn't appear until 1925.