I just created a partical emiter, parented it to the bullet, and created an Sine expression, that the scalepp is controled by the time. Just create a simple creation expression with the starting scale, and create a runtime expression using the sin function. Hope this will give you some ideas, it doesn't create "disc" but you can use blobs, as the particles, and it will look like the matrix. then, you can write another expression, that controls the color pparticle, and you can make one bright green, another one bright red, then render, create a displacement map when compositing, and it fits in nicely, I used this method for a shot few second clip that I am including on my demo reel. I have it rendered and composited, but I am going to wait to show it untill my entire demo is done. THanks,
Brian
Hope this helps at all.