I haven't played VB Aurora in a while and only started playing around with Aurora C# recently, but one thing I seem to remember is that you might want to over-engineer the range of your beam fire cons.
If I read the stats correctly and assuming you left range-bands at the default 10k and target speed at the default 4k, then your Railguns have a chance of hitting a target moving at 4,000km/s at 30,000km of 53% and at 60,000km of 6%.
Now, if you'd mount a BFC with a range of, say 96,000km maximum range, you'd get that to-hit chance up to 69 and 38% respectively.
Unless I'm mis-remembering or missing something, of course