"Tungsten is a very poor conductor though, hence its utility in light bulb filaments." Actually it is one of the better conductors. Material Resistivity Conductivity Silver 1.59×10−8 6.30×107 Copper 1.68×10−8 5.96×107 Annealed copper 1.72×10−8 5.80×107 Gold 2.44×10−8 4.10×107 Aluminum 2.82×10−8 3.5×107 Calcium 3.36×10−8 2.98×107 Tungsten 5.60×10−8 1.79×107 http://chemistry.about.com/od/moleculescompounds/a/Table-Of-Electrical-Resistivity-And-Conductivity.htm The reason it is used in filaments is not it's resistance but it's high melting point.
“Actually it is one of the better conductors.”
Well, it’s worse than most commonly used conductors, like copper, aluminum, or gold. You do have a point about the high melting point though, but the combination of relatively high resistivity and high melting point might not be good if you are subjecting it to a large magnetic field. A little too much induction, and while the tungsten won’t melt, it will emit black body radiation and might melt the railgun!