Looking through the files I found a bug relating to the setting for the cannon shell firing speed.
In railgun-turret.lua, line 21 reads
if settings.startup["kr-cannon-shell-range"].value ~= 100 then
whereas it should be
if settings.startup["kr-cannon-shell-speed"].value ~= 100 then

It would rarely have an impact, but if the range gets set to 100 and speed to something else the settings will break. Otherwise, as long as the range is something other than 100 the speed will be adjusted to whatever the setting is, and it seemingly works.

BTW, why is the railgun turrets range defined as the same as the cannon shell, why not something different. They don't have to have the same values, and the rocket turret doesn't have the same range as rockets.