So... near-free munition guns to protect your investments. Getting defensive makes a bit more sense for this world, since they have to constantly defend against the planet and other colony. But then again, is the best defense a good offense?
At any cost, what exactly is a coil gun? Because I think of one of those Tesla coil's shooting electricity, which would just be a Thor Jr. What about, and this may be a bit primitive, but some sort of catapult, or siege cannon? Though that would use ammunition.