When the rogue NID agent opens fire on the Air Force SpecOps unit. with a full auto 9mm Beretta. he empties his magazine with the first two volleys, as evidenced by the pistol's slide being locked open. Yet he turns and fires a third volley of rounds to blow the lock off a door without having time to reload a fresh magazine.
Before the opening credits, while Sgt's Harriman and McKenzie are observing the Stargate, the Iris is open. It is standard operating procedure for the Iris to be closed at all times unless a security code is received.