“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!
“Well, it’s worse than most commonly used conductors, like copper, aluminum, or gold.”
Well, copper and gold melt at just under 2000 degrees F., and aluminum at 1200 degrees F. Tungsten is over 6000 degrees. I suppose you could use a copper projectile, but obviously not aluminum or gold. aluminum is too reactive with air as is calcium. Both would oxidize traveling through the air.
Tungsten is the best choice... And it’s relatively cheap.