Which would be better for firing a 7.82 mm projectile faster than 4,000 feet per second?

I'm trying to see if a Coil Gun (Gauss Gun) or a Rail Gun would be able to do this more efficiently. Also if possible can you tell me how much electricity this would require? Just in case, let's say the projectile is about 20-30g in weight. Thank you for any help you could offer me.