the easiest solution to that problem would be to create different weapon types, for example: Railgun I,II,III etc, each one of them with an slightly different loading time, probably something less than a second (for example, the railgun I takes 10'' to load, the II takes 10.5, the III 9.3, the IV 11, and so on)
Either that or you could build an script that would delay the shots manually and produce that effect, although I strongly recommend you choose always the simplest solution to a problem.