Hey, sorry about that. I must've missed your post. You can instance geometry with particles. For instance, if you wanted to do a swarm of bees, you could have one bee model and instance it with particles. Each particle would become a bee.

So, you can make a particle emitter, set it to emit just one particle at a time, at the right speed and so on. Instance your laser beam geometry with it. I believe you select your object first, and then the particles, and Particles > Instance (Replace) or something similar. You would animate your original laser beam geometry somewhere off camera and your instaced copies will mimic it. Parent the emitter to your gun and it should follow it wherever it goes.

As for the looping path animation, I believe you'd need to do it fairly manually. When you attach a motion path, you'll notice that two numbered handles appear on the path, indicating the location of the attached object at the start and end frames. You can add additional keys to this. So, For example, if you have an object on a path that starts at frame 1 and ends at frame 100, if you go frame 200 and key the U Value under the Motion Path Channel Box options, it adds a new numbered indicator. You can then grab these indicators and move them around.

Hope that helps some.