Other mistake: Shooting two forty-fives at once is hard. Willis must think so too. One gun fires blanks and the other gun operates like a real pistol, even emptying out shells, but is not firing. This is very noticable in slow motion during his first standoff.
Other mistake: Upon entering the bar to rescue the bartender, Willis shoots his first victim clean through a window. In slow motion you can see the gun is never fired and yellow flash is edited in.
Factual error: The phones in town are crank type or candlestick type that require an operator,as mentioned by the hotel owner at the beginning of the film.John Smith calls Georgio at the telephone office by dialing the number,impossible on a system with no central office switching equipment.He would have just used the patch cords and pressed a button to ring the phone.