Does the spear resting on the rail not cause friction on the spear and slow it down?
When in the water the rail and spear are both wet. Once the spear gets going it will slide on a thin film of water, which eliminates the possibility of it touching the barrel. A well-used railgun shows no wear in the rail, which it would show if there was significant contact friction. This is similar to the way that a slipper bearing or a beach skimboard work.
