A lot of movie people go out and shoot their own footage of muzzle flashes. They get the kind of guns they need and take them to a firing range, set up the background and lighting and shoot the guns.
Others just use blanks and actually use guns on set.
Others have a digital artist paint some. A muzzle flash is only on the screen for a frame or two; a bright-coloured solid, masked and feathered, is often just fine.
- The Great Szalam
(The 'Great' stands for 'Not So Great, in fact, Extremely Humble')
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