One of the big differences is that gas chambers are only useful for killing prisoners while there is no indication whatsoever that railguns will be used to kill

One of the big differences is that gas chambers are only useful for killing prisoners while there is no indication whatsoever that railguns will be used to kill prisoners. (That said, if it were my execution and the choice were given to me, I would of course chose the railgun! Suffocating on cyanide gas doesn't seem like much fun, I'd rather be vaporized by a hypersonic artillery shell, if it's all the same to you...)