Re: I heard something about an impervious fortress...
These weapons are intrinsically MORE accurate than any other. Give it an innate penalty to hit to make the flavor match the crunch.
Running: Ruceeglaelsktinag ICOOCMap
My Dream Campaign: ICOOC No Map Right Now.
For everything else (including my extensive homebrew) see: Extended Signature My Homebrew is meant to be used, but, if you do, PLEASE tell me how it goes.