Ok, because an image gives more than a 1000 words I've decided to do some tweaks. http://img33.exs.cx/img33/1364/flash.gif
First I've mirrored it. A star of a flash of a light (and that is what a muzzle flash really is) is farely symmetrical. It doesn't shape an X star, thus was mirrored vertically.
A flash should be very bright, thus I've used plenty Light tweaks including the Lightness Up Retouch in the middle (that's where it is at it's brightest)
Then I removed the dirt around the flash that You made using the lousy density airbrush. I don't know what that is (gun powder? sparks?) but it's not good IMO.
It also looks You didn't use the smudge tool that makes an impression of radialy spreading rays-which make a decent "flash star".
I hope I helped in some way.