The presence or absence of the flash depends on several factors. Quality and type of powder, barrel lengh, presence of a flash hider on the muzzle, etc.
If there's a flash hider installed, you most likely won't see any flash. Some powders contain flash retarding chemicals added for that exact purpose. Barrel lengh is also very important. A long barrel gives the powder more time to burn, while the bullet is still inside the barrel.
Here's a quick video of a cool flame throwing Krink:
So is not that simple. Things have to be checked for individual type of gun and ammo.