Continuity mistake: When Buster is shot, his hat with the hole in it disappears.
Continuity mistake: When Buster approaches the table, we see the glass is about 1/3 full. Next shot it's 2/3 full. Then it's picked up by the chap with the goatee, But it reappears on the table at "weapon." Next, at the wide shot, it's empty, (as are all the glasses, also the other glasses were full, now they are empty).
Factual error: When Buster joins the card game in the saloon, he looks at the hand of the player that had just left. Given the circumstances in the saloon, the cards cannot be spot clean and white as fresh snow. Also, they seem to be plastic cards, which did not exist yet back then.