Continuity mistake: When Sam is counting to five when riding his horse, he runs into a telegraph pole and loses his guns in the process. But when he catches up with Bugs on the train, he is holding his guns again.
Continuity mistake: When Bugs and Sam start their duel, you can see there is a glass at the end of bar counter. But when Bugs goes to the end of the bar, the glass has disappeared.
Continuity mistake: When Bugs shoots Sam in the face when trying to shoot a can, the can lands in front of Sam. In the next shot, the can has disappeared.
Continuity mistake: When Bugs is performing his shooting stunt in the saloon, you can see the entrance behind Sam has nothing between it. When Sam tells Bugs he's missed, we cut to Bugs who says "Wait!" and then return to Sam, and this time there are doors between the entrance.