Factual error: The exchanges between the bad guy pretending to be an air traffic controller and the pilot of the doomed aircraft are not even close to realistic. Air traffic control communication is almost its own language. The FAA handbook says, in part: "Brevity is important, and contacts should be kept as brief as possible. Jargon, chatter, and 'CB' slang have no place in ATC communications."
Factual error: Transport aircraft do not have ejection seats; only fighters, bombers, and attack aircraft have them.
Answer: If you listen, he says something to the effect of "I know I had that guy in my sights", meaning he is amazed he missed. So he checks the bullets in the magazine to see if that's the problems. Blanks are simply shells with no bullet that are crimped shut to hold the powder in. The difference between blanks and live rounds is very obvious even at a glance.
Grumpy Scot