It could work like a capacitor, charges up using a lot of energy but then shoots with the charged up energy before needing to reload, that would mean you still have to have a reactor but it wouldn't be a constant draw so your armor could still use other modules like roboports. Railguns could also use a system like the personal energy shock defense module where you get an item that you use to activate the railguns so then you could have them be an alternative weapons module to spice things up
