d24454_modern
Explorer
I think I’d be ok with a d14 for an average weapon and 2d7 for a good weapon.Honestly, that's not that useful IMO. Weapons with a damage range of 1-12 are already starting to get swingy because you have an equal chance of rolling a 1 or a 12, and that tends to make them a bit unreliable, where a 2d6 tends towards 7 rather than the extremes, and you can't roll a 1. That's going to get worse the more sides you add to a die. So a 2d8 or 3d6 generally tends to be a little better for increasing damage even if you're more likely to hit the averages.
From a lore perspective, you could justify it by saying that the weapon is an Exotic one.