Revealing mistake: When Potter starts shaving at the morning of the Indian attack on the wagon train, his mirror falls off the post, and as he bends down to retrieve it, an arrow embeds itself right above his head. If you look closely in that scene, you can see a length of targeting wire used to guide the arrow sticking to the post above Potter's head. (00:37:10)
Continuity mistake: When Sam goes to the bottom right door at the end of the in-and-out routine, you can see that the handle is on the left hand side of the door, but in the next shot it is now on the right hand side.