I think that making assumptions about this would not be the best way to proceed. It surprises me that you would have to drill something out as you have described the situation but there are all sorts of configurations. If you are determined to do it yourself, I'd call upon either someone with the "Amateur Gunsmithing" book or hope that a friendly smith sees this thread. Not knowing the gun or its style makes it hard to advise.
Are you able to post a picture of the gun?
In general, retracting firing pins can have a flange or other means of stopping inside the action. What year is your double approximately? If pins are involved, I would almost rather attack them with a small hammer and driver to try to get some purchase on the metal. If I used a drill, it would be in some kind of press and an iterative process to see what happened.
