Depends if you want it animated or still. For a still image try using a series of flattened P5 spheres so they are disc like. As above adjust transparency and refraction. I would also think about adding some 'wavy' noise into the bump channel and see what that looks like. For an animated effect you probably need the flattened spheres to appear as a trail behind the bullet. A Python script might be the solution there but I'm not very converant with Python - just seems outdated having to write scripts to achieve effects.