The issue with older guns, assuming you can hold the pressure down to reasonable levels, would be the quality of the steel and the thickness of the barrel walls. Danger would be a potential ring bulge. That is reduced with 1) more open chokes; and 2) smaller size steel. It's increased with 1) thinner barrel walls; and 2) lower quality barrel steel.
A lot of old American 12ga doubles would likely be OK with no choke, because they often have pretty stout barrels. Expect I'd risk it with something like a Stevens, Lefever Nitro, Hunter Fulton, etc. Would probably hesitate with any kind of American classic in really nice condition, especially if higher grade.
