[mcguyver]

You could use the same power to operate the coil as you use to run through the contacts. An automotive relay (12v DC) will operate at lower voltages, like 10.8 or 9.6v or whatever you are using. But, for an 160 m/s setup, you should be using at least 12 volts, the motor will need to see that kind of potential do deliver the torque needed to drive that spring.

Now, a relay sounds good in theory, except there's one little problem. It doesn't stop arc formation, not one little bit. All it does is move the big arc from your switch contacts to the relay contacts. They will arc as well, but at least they are external to the mechbox, so replacemement will be easier. Another drawback is time. When you energize the coil of the relay, it takes time to close the contacts. Even though this time is small, when added to the initial spool-up time of the motor and mechbox, this only adds to the trigger delay. I don't recommend the use of a relay, it has no real advantages.

I think what you want is a transistor. They are what's known as "dry" contacts, meaning there is no physical gap betwen them, so no arc forms. You can use MOSFETs or a wide variety of other types. There's lots of info out there if you want to build your own switch device.

Arc formation is not just about causing damage to the switch contacts. in a closed system like an AEG, the formation of an arc requires massive amounts of energy, energy that damages contacts, but also is not being used by the motor to drive the gun. This is why guys see increses in ROF just by installing dry contact systems.