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.
Although the retrieval team is billed as "US Navy SEALS," they are addressed in the military ranks (such as "captain" and "major") used by the Army, Air Force & Marine Corps.
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.