I don't understand weapons stats

[Miraculix]

I think (I'm actually pretty sure), the 2 sets of damage amounts you see on these weapons is 2 different types of damage. Probably slashing and piercing.

So for:

45-57 attack 91-103 with a (+6) bonus, it would mean that it deals:

45+91+6 = 142 up to 57+103+6 = 166 damage per hit, hitting for that damage at fast speed. The damage would be composed of 45-57(+6) piercing and 91-103(+6) slashing damage. (The types of damage might be wrong, you need to check the little icons next to the numbers)

Here's an explanation of the different damage types in this game:

http://regnum.wikia.com/wiki/Damage

Correct me if i'm completely mistaken here