Why not simply "Metal Alchemist"? Why is Edward Elric known as the 'Fullmetal Alchemist' not simply as 'Metal Alchemist'? Is there any reason besides the names sounding better?

I've only watched the 2nd episode of FMA brotherhood.
I don't think there's a reason beyond the "Cool" factor.

はがね (Hagane) translates to "Steel" or "Metal", so I don't see a real reason.

Fullmetal, refers to objects that are completely made of metal, that they aren't hollow or are composed of other, non-metallic materials.