I've long thought that some kind of Fabrial based railgun or coilgun should be possible given what we've seen of Fabrial science so far. Personally I'm a fan of a coilgun version using attractor or repulsor (ok these are theoretical, but if you can attract something, the opposite is also possible) Fabrials which could then be activated in sequence to accelerate a projectile down the barrel. The only question for this weapon type is whether the control systems exist to do this correctly. (n.b. the first operational coilgun was made in 1904, so it isn't that complicated.). Fabrials would have a big advantage over current railgun/coilgun designs as they wouldn't require the large amount of power currently required in reality..