My opinion only!! I believe if this is a crack, you should be able to see a corresponding place in the bore directly at the place of this crack. If a bullet was stuck in the barrel and another bullet was fired behind it, usually you can see an egg shaped spot in the bore where the second bullet compressed up against the rear of the bullet in front. Normally you can also gently slide your thumb and forefinger along the barrel and feel the egg shaped bulge if one exists. One some barrels, especially the more slender ones, you can look down the barrel and see it.
This mark is very near the frame of this short barrel, and I see absolutely no sign of any potential egg shaped bulge in the barrel, but this is not a spot where it could easily be seen from the outside. IF there is such a bulge at that location, you should be able to feel it inside the bore by fitting a tight patch on your bore cleaning rod and gently sliding it down the barrel. If there is such a bulge, normally you will feel a slight reduction in the resistance present as you move the patch down the barrel. You should also check closely all around the frame where the barrel is attached as well as the forcing cone area to see if there is any sign of a crack anywhere in that area. I doubt you will find one.
I also believe this is just a scratch, and that it happens to be deep enough to allow you to feel it with your fingernail. And I doubt you will see anything inside the barrel or feel any difference inside as you pass a tight patch through the bore. Since the mark is so close to the forcing cone area, you can lay the rod down on the side of the barrel and make a mark on your rod at the exact location of the mark so you can tell if the patch is at the mark or is passing into the forcing cone area. The mark is close enough to the cylinder end of the barrel that I also believe if there is a crack there, with a clean bore and a good light to illuminate the area, you will be able to see that area underneath the mark from the forcing cone end. I'd want to satisfy myself that this is just a mark, but I would be very surprised to find out that there is a crack there. Good luck with your investigation. Let us know what you find.
FWIW, many barrels that have been "egged" continue to shoot just as well as they did before it happened, especially if the bulge in not near the end of the barrel. Nobody wants an egged barrel, but if it still shoots well, then it's still a good shooter!!
