Here's is my attempt to make a BF3 muzzle flash. It looks good mostly on modded skins, especially on the ones with custom particles.
Obviously it doesn't look as good as BF3, BF3 Muzzle flash is fully based on particles, while CSS is just a sprite.
My new (more crappy) preview:
New version is uploaded. It should be much better now, with better muzzle for weapons without custom particles. More size and muzzle placement variation, PLEASE, redownload.
UPDATE 2 (FINAL!)
This is the last update. The only thing that changed is the texture itself, which is now less detailed (which looks better) and heavy desaturated, I looks prefect now, very similar to BF3. Screenshots are updated. I would be glad for new preview, because I make crappy previews.
Now it have better saturation. Sorry, this is definitely last fix. I'm 100% sure that there is no way to make smaller guns have animated texture, it can be only done for rifles that use muzzleflashX.vtf texture.