But that is where we are heading?All you need is a reliable power source and you have a portable rifle.
I wouldnt go so far as to say that, but I would say that the power supply may well be the biggest hurdle.
Talisker makes good points on conductors. Making a conductor capable of handling the currents required to launch a projectile at 5000 fps and survive to do it a second time is a major hurdle.
What we may see first is a man portable shoulder fired rail gun anti-tank weapon that is used once and discarded.
Materials that can survive the high current loads are the major problem to overcome in a man portable rail gun. This is why I think a disposable man portable weapon will be the first on the battle field.
It may take high current room temperature superconductors to make a rail gun battle rifle a reality.