If your level is pretty dark, you could try using additive blending. Otherwise, the blurred alpha channel TPX described should do the trick.

I think it would be better and faster to create your own muzzle flash. It doesn't have to be detailed or beautiful... we'll only see it for a fraction of a second.

He would still get a black box around it. The *easiest* way, without worrying about alpha channels, is to set the blend mode as such:

I don't know how you'd do this in Dim3...