So this is kinda my process when it comes to coming up with muzzleflash textures.
First off, gather reference. Get a sense for how you want the flash to feel. Watch videos to get a sense for the timing.
Look at other games as well. Find a game that you really like the muzzleflashes in and take screenshots of them so you can study the texture design.
I’ll build the textures either by hand-painting them, compositing reference photos, or using stock footage. Get creative - go out with a camera and film firecrackers exploding for use as muzzleflash material reference.
These are some of the flash materials I created over the course of one project. I use sequenced textures in groups of either 4 or 8 that the particle system can randomly cycle through. This will give you the variety you want in the flame.
Most of the process is iterative so I’d experiment with different muzzleflash textures to get a better sense of the feel I want.
When it comes to the particle system I’ll usually split the system between a circular flame billboard for the core of the flash, then the longer directional billboards (with the directional textures) for the longer flames ejecting out the front or sides.
https://www.youtube.com/watch?v=nCbOxTWj6bc&feature=youtu.be
If you keep the timing tight on the flash it’ll give you a punchier feeling effect, especially if you include the other elements like the sparks and smoke. Of course it all depends on the artstyle of the game and the feel you’re going for.
The corridor video posted above is a really good breakdown of how to get the timing and details of the flash right.