That gap is normal, and should be there. Some where in the vast archive a real gunsmith described in awesome detail the road all SxSs will take before comming off face. If you could not see that gap, then it is called being on the flats and it's time to have it serviced. Try this: take a peice of printer paper and close the action on it, on the breech. If you can pull it out, it's just off face. If it's snug, you are fine.