Firstly, make Chaos only for swords, and this new gear will be like chaos and mad bomber, except it's attributes will be for handguns.
Gunslinger Hat ---> Sunset Stetson ---> Crazy Chapeau
Gunslinger Sash ---> Sunset Duster ---> Crazy Coat
(Not the best names I'll admit, but that's the best of my imagination, feel free to suggest names).
So Chaos sets' bonus only work for swords.
This set will be elemental defence. This set will also have the same elemental defence as the Mad Bomber set, alongside with Fire, Shock, Freeze and Poison -2 Penalty on each piece.
That way Mad Bomber or Chaos Set will need changing. All you have to do is add another Risky set for either swords or Handguns and then that makes Mad Bomber useful.
I don't this is a good idea. Chaos was designed to be a general purpose set. OOO did that job a little too well, but the answer to that shouldn't be to destroy chaos. If chaos was changed to have these stats, everyone who owned it (or at least all the hybrids) would be in an uproar over it, since that change would destroy their loadouts and strategies. Having an offensive sword-boosting armor evolve out of a general purpose defensive armor also doesn't make much sense.
IMO, a better approach would be to nerf chaos so that it isn't OP but is still able to perform in its current role, rework mad bomber, and add a mad bomber equivalent for swords and guns.