> One of the major problems would be the absolute destruction caused to those you convinced to line up for this weird tango.
As long as there is an earth-shattering kaboom, I don't see the problem.
That said, if I ever introduced this idea in a game, he would probably introduce me to a tarrasque (for non-DnD people: the tarrasque is pretty damn near invincible and a railgun would probably just piss it off).