OK had a look at it...sort a
Stock Game
Modded (fast quick fix :p )
As you see the (fire ball) is not as big as in the pics posted by "SingeDebile"
I am not sure if changing the size of the texture actually makes it bigger...don't look like it so far. Did this quick and dirty just to see if I could...and well...it will for sure look more impressive in the dark

.
To get something as awesome as in the pic in the 1st post i think we need to tweak something more...what? no idea at the mo, but something controlling the size of the muzzle flash...for short
DOWNLOAD LINK:
http://files.filefront.com/MUZZLE_FL.../fileinfo.html