I have seen that on one vintage double which had a lot of X bullets (the ones without the grooves) shot through it. Then the rifle was pointed toward the sun, the rifling pattern could be faintly seen on the outside of the barrels.

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Butch, that is good info. The 20 or so rounds I fired through the rifle were loaded with Woodleigh softs and just 110 gr. H4831. The owner of the rifle was out of ammo, but said I could shoot reloads through it and that he preferred 114 gr H 4831. When I looked up the load it seemed a bit hot, so I downloaded, figuring that if the bullets were 6" or so apart and not crossing, the load could be adjusted. But it was just the opposite. With the light load the bullets were crossing badly.

One other thing about that gun which I did not remember when I wrote my post last night is that the right firing pin liked to get stuck in the OUT position. So before the gun could be reloaded and closed, I had to press on the firing pin with the rim of an empty case to make the firing pin go back inside the action.