Does anyone know what would be considered a normal sound/light experience the moment a 1,200A/480V breaker trips? The reason I ask is because we recently had a 1,200A/480V breaker trip and it was described as a bright flash of light that came out of the panel and an extremely loud bang -- described as a shotgun going off. We suspected this was an arc flash; however, when the breaker was subsequently inspected there was no damage observed of any kind. The electrician stated that if he hadn't been there to see/hear the trip, he would have had not suspected anything abnormal whatsoever. Could this have been just normal for a breaker trip of this size?

Sounds normal.

The energy in breaking the fault has to get dissipated some how.
The magnitude of the 'fault' current being interrupted will impact the effects.

Do you know how much current was flowing? Breakers can really only successfully clear a maximum bolted fault only once, and still be able to be reset.

No we don't know the current, nor the source of the overload at this point.

Thanks for your feedback that this sounds like it might have been a normal event.

Related question -- for a breaker of this size is it normal for the breaker handle to not move very much once it trips? Also, once it trips, is it normal for the handle to feel sluggish when opening and closing, almost like the handle is moving through a thick fluid?

Breakers are designed to be 'trip free'. This means the breaker handle is 'disconnected' from the tripping mechanism until the breaker has been reset.