Railgun Mk V and Mk VI both require Mass Drivers III
Railgun Mk VI is dominant
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Railgun Mk V and Railgun Mk VI both have the same tech requirement. When I saw this in the tech tree window, I was wondering what the tradeoff would be. Space vs Cost?
But there is no such tradeoff; they are identical in cost, damage and sizemod. The only difference is that Railgun-V is size:6 and Railgun-VI is size:5.
Therefore there is no reason to ever buy a Railgun Mk V. It could even be removed from the tech tree.