When watching the robots altering Jake's helicopter, the Major tells Cage to take a shot. Cage is clearly using an M-16 variant with a standard "peep" sight but when he his sight picture view is shown it is as if he's looking through a scope with red cross hairs.
Some weapons supposedly fire a round without the weapon action cycling to eject the empty cartridge. In a few scenes the M16's are shown from the front and the muzzle are solid which means there is no place for a projectile to exit and are obviously prop guns.
At the end of the movie when the team are trying to trap the robot, they spend quite a while out in torrential rain, yet their hair, clothes etc. remain completely dry, even as the (CGIed) rain pelts down upon them.