I've updated my bullet engine a bit and I'm soon finished with that part, just missing some small programming stuff that will make my life easier.
I've added a dust layer that I can turn on/off with a timer (having it on all the time affects performance drastically).
Also added a waypoint system that lets particles follow a path. And finally I've added gravitywell support, nice if you want enemies/bullets to avoid/attract areas. There are tons of other stuff I've added, but I'll focus on showing these for now..
Here's a demo:
http://www.flashbutler.com/projectile.html
You can click anywhere to add a waypoint, the red circle following your mouse is a gravitywell that pushes particles from it.
Also, If you add more than 256 waypoints the particles will stop (doesn't support more than 256 points per waypoint path).
Mind the performance is affected now because I'm using the dustlayer all the time, normally it should sit nicely around 60 fps with it turned off.