Well I think you have been given a plethora of good ideas here and one of them is bound to work for you and your group. One other thing; keep in mind that whatever you decide to go with will apply to your monsters as well as your players. It'd be conceivable for some cultists/Red vamps/etc... to start profaning bullets and having them cause profane damage. That might be a bit of a shock to the players the first time a normal bullet wound starts to cause a lot more damage as it attacks their innate goodness. Again, it might be something to hammer out with the players but its certainly legit.
