If it was a ‘real’ gun as alleged, it must have been a real rattletrap, and why a prop like that would be let onto an insured movie set in that condition, and in the custody of a ‘trained’ armorer, is mind-boggling. But I only watch Hollywood pablum. I don’t live in it.
I don’t think the armorer was up to the task. I wouldn’t be surprised to learn that crew spent some time fanning the gun when they were playing in their off time. You saw how solicitous Schneider was about caring for the pistol that belonged to his friend. I’ll bet the opposite was true of people playing with the prop gun.