Muzzle Flashes

This looks like a fun topic. Using simple logic and a bit of Physics, these issues are easy to reason.
In the case of firearms, the flash is fire and its something burning.....powder. The bigger the flash outside the barrell, the more the powder is burning
OUTSIDE THE BARREL. A really huge muzzel flash represents a really inefficient use of powder. Not a real problem, just waste. On the other
hand, no flash can possibly mean there is a bit of a problem. It can mean perfectly efficient use of powder or not enough. If not enough, the powder
is consumed within the barrel before the bullet leaves, allowing a reduction in pressure and bullet velocity. The ideal goal would be to have the
last dregs of powder burning as the bullet leaves the barrel. The short story though is that it is better to err on the side of excess powder than not enough.

Next comes the issue of powder burning rates. Generally, you want faster burning powder for shorter barrels, or the converse. To illustrate, lets use an
example of the 223. The M-16 does have a flash but not what I would consider to be in the Hollywood class. However, take the round out of the M-16
and put it in an 11 inch barrel like the Thompson Center uses for the 223. The flash is approaching Hollywood criteria but the bullet velocity has gone
away. Also look at the flash in the photo posted by Ulvetann. That is from a weapon firing standard 223 BUT HAS A 7.5 inch barrel. You sure do
get a bit of Hollywood there but notice they do not brag about its ballistics. That is an entertainment piece, but thats it. What can you do with it after the show ?
The best example of all is the .22 long rifle. In the target style rifles (on the order of 20 inch) have almost no visible flash and may even be allowing
the bullet to cease acceleration within the barrel. Put the same round in a North American Arms .22 derringer (1 inch barrel) and the flash is readily visible
in daylight.

Nobody seems to be addressing a more significant issue. Sound. Yeah, the bang thing. Yes, a supersonic round has a sonic crack, separate from the bang thing.
The components of the sound source is high pressure gas escape, and, YEP THE FLASH. Powder that burns outside the barrel is burning at a supersonic rate
and is a significant contributer to the bang, and the frequency of the bang. Try this experiment. Fire a .22 long rifle in a long barrel rifle, then the same round
in a short barrel pistol. I recommend hearing protection especially for the latter. For those who like the flash/bang, it generally means you have traded
bullet performance for a light and sound show. Maybe that can be desirable. In Hollywood, its all show, no bullet, so all the powder is used for the show.
The USS Wisconsin is almost a whole different topic. When using an explosive as propellant, as opposed to fast burning class B powders, you always err on the side
of safety. Last time I checked, those 16 inchers were using an explosive (black powder) and not enough powder there would have serious consequences.