How does Damage Range work?

What I want to do is add randomness to my damage - for example, I want to have a skill that can hit from 1 to 10000 damage.

What I would think to do is set the Damage Range of that skill to a large number.

The result of doing that is: Skill does WAY MORE damage, but consistent and in no way randomized.

How would I accomplish what I'm looking for??