Other mistake: When he arrives at the club he texts "I'm here" and receives the reply "bathroom" but the texts are on the wrong side of the screen. It looks as if he replied "bathroom". (01:20:10)
Factual error: When Kersey finds his throw down gun and proceeds to practice with it, a bullet ricochets back at him. Lead will reflect off objects and continue in the same general direction or flatten out on a surface but will not bounce back at you. If it did, indoor shooting ranges would kill all of their patrons on a daily basis.
Factual error: When Dr. Paul Kersey pays a visit to Joe Gannon, the garage mechanic, Kersey slices open Gannon's leg with a scalpel, then pours automotive brake fluid into the wound. The brake fluid sizzles and foams on contact with the blood, which is chemically impossible. Brake fluid is simply hydraulic fluid formulated for extreme temperatures. The diethylene glycol in brake fluid may be toxic and may sting slightly in open wounds, but it does not violently react with blood and sizzle like acid as depicted in this film. (01:14:45)
Continuity mistake: When Fish gets shot in the leg and runs out of ammo, we see him on the monitor still trying to shoot in vain. When it cuts to him, the slide is locked back and we see him release the slide and try to shoot. But in the next shot of him, the slide is once again locked back. Since we know he's out of ammo and he didn't reload or fire the gun, the only way for that to happen is if he manually pulled the slide back, which he didn't have an opportunity to do (not that it would even make sense to do).