Revealing mistake: When Mason is having his hair cut, after finishing up, he is talking to Womack and turns his back on him. If you look at the back of Mason's neck, it is clear that he's not just been freshly shorn; there are whorls of hair just above his collar. (Either that, or the barber was terrible at his job).
Revealing mistake: During the car chase, when the first FBI car flips over, the device used to flip it over is visible on its underside. (00:45:55)
Revealing mistake: During the big chase scene when the tram is out of control as it hits the last car and blows up you can see rubber tires on it, specially added to let it go on tarmac.
Revealing mistake: In the shower room massacre scene, you can see a bullet casing when they show one of the dying Navy SEALS really close-up. If you look carefully, the end of the casing is crimped, which is what a blank round's casing looks like. A real bullet casing would not be crimped at the end.