The problem is not the metal bristles in the boresnake or any brush for that matter. Its repeatedly pulling the cloth over the sharp edge of the crown that causes the damage. Think using a rope to cut down a tree VIA friction.
My Nylon bore snake sure as hell ain't cutting steel. Mild tempered 416 stainless has a brinell hardness of around 388 and nylon rope of a boresnake has a hardness of approximately potato and again certainly less than brass bristles.
Methinks were not gonna agree on this one.