I agree that it's probably not going to happen today, but it's well within reason to expect that'll be something that's feasible in the near future. Remember, each of those rounds is packed with the gunpowder needed to propel it to a target. A gallon of blackpowder contains a LOT less energy then a gallon of diesel, by an order of magnitude.
A railgun round is just the actual payload, so it's small. Every cubic foot saved in weapons volume is a cubic foot that can carry high energy density diesel that can be converted into power to propel the round with terrible force at the enemy.