Lead is too soft..
to damage steel, a much harder metal than lead.
But, buckshot pellets should deposit a lot of little bits and pieces of lead all through the lands and grooves of a rifled shotgun barrel.
Also, every buckshot pellet that comes in contact with the lands and grooves will be "deformed", i.e., no longer a perfectly round sphere. These deformed pellets will all become "flyers", and leave the normal shot pattern, probably bumping into other pellets in the pattern, deforming them, resulting in what is known as "a blown pattern".
I don't known if such a blown pattern will result in a donut hole configuration, or not. I would expect very erratic patterns, with no two the same, and lots of holes that would make for ineffective results.