This effect means that, at least with current materials technologies, you would have to frequently replace the rails of your gun, which is a bit of an issue on the ground in a combat zone. If you look at videos of the General Atomics Blitzer railgun platform firing, you can see a large fireball expanding out of the weapon's muzzle, which is the plasma generated by the rails and armature burning off. One issue, however, is that when a railgun fires, the massive electrical output bridging across the armature causes an amount of the metal making up the rails and armature to be converted to super heated plasma. The General Atomics Blitzer railgun has already demonstrated higher muzzle energy by far than its contemporary naval guns, for instance.

If you discount the power requirement, a railgun could most likely achieve velocities significantly higher than a modern 120mm chemically propelled gun. In future, though, these systems could prove to be the next generation of propulsion for high velocity penetrator rounds. In terms of current technology, we're not quite to the point of electromagnetic weapons being practical on armored vehicles, mainly due to power generation and storage limitations.

Modern day tank round