Other mistake: If you find a special ammo type in the game and swap your regular ammo out, the gun becomes unloaded and you have to load the new ammo type in. But say if you're doing it with a revolver like the Nagant, you will start unloading empty casings out of the gun to put the new ammo in, as if you had shot all the old ammo out of it even if you never fired a shot and the gun was full of fresh bullets before swapping ammo. The same reload animation of ejecting spent casings.
Revealing mistake: The character Sheriff Hardin is wearing a Sheriff's star badge on his chest. His coat has a flap on the opening that overlaps it a little causing the badge to clip through his jacket half-way.
Trivia: In one of the shacks, the devs hid an Easter egg referencing Back to the Future 3. In the shack, there is a tarp with the shape of the DeLorean underneath it. Also if you look in front of the DeLorean, on the table is the model train set similar to that of the train set used in the movie to demonstrate the time jump in Doc Brown's model.