Ah, but a Railgun is a magnetically powered weapon, so ammunition makes loads of sense.
A little impractical, though, at least rules-wise. Railguns are hindered enough without giving them a certain number of shots. Although it WOULD give another practical use for a Freighter, as it could also carry Munitions Stores and be able to replenish just like it does with Missile Barges. So I suppose that kinda balances out. Go ahead and try it like that, massacre, and let me know how that works. We'll playtest them without ammo and see how that goes. Once we hear from multiple parties, we'll converge to discuss, and change whatever needs changing. They are terribly experimental at this point, but I'd hate to see them removed.
"In a mad world, only the mad are sane." - Akira Kurosawa