Unfortunately, a great deal of the losses stem from resistive and friction forces and not much can be done to mitigate them. There are a few simple things I could do to decrease losses. For starters, Aluminum has a very high coefficient of friction which means it has higher losses than many other metals. The reason I used it for the projectile is it was cheap and easily machinable. In the future I will replace the projectile with a more suitable metal. There are a few other idea's that I am going to test to increase the efficiency of the railgun, but they are worthy of their own articles.
I have built a multistage coilgun before! The problem with coilguns is you need a very large inductor if you want to get the projectile moving a decent speed. This leads to multiple problems since inductors resist changes in current. Basically, it is very difficult to turn them on/off fast enough to achieve decent speeds.