Factual error: Miller rigs his booby trap by attaching the wires from the bomb to a pole down which a metal runner slides, so that when the runner touches the wires it completes the circuit and detonates the bomb. The trouble is, the pole is made of steel, and steel is very conductive indeed. Miller attaches the exposed end of the wire to the pole without any insulation or gap. The circuit will actually be completed when Miller attaches the battery, and he and his booby trap will be blown sky high.
Factual error: The rifles that Jake Cutter has Paul Regret dig up are Henry repeaters, or possibly 1866 Winchesters. Either way weapons unavailable in the period depicted in the movie.