I think the primary difference is how many longitudinal subdivisions we used. I'm looking at several of your forward railguns and there are a lot of subdivisions length-wise, but given the nature of their design there's not much to be done about that without making them look really derpy. I'd watch out for any unnecessary subdivisions. On their front-most faces there's an edge cutting a ring in half that doesn't need to be there.
Also, looking at the engine/subsystem greebling, that's a bloody fantastic job you're doing in there, just don't have 12 subdivisions down pipe segments that are straight. Those can all be represented by 1 continuous cylinder until they reach the curves. Also, you can dial back the azimuthal edge count for smaller pipes and it'll still look fine.