I saw a cut, or circumcised shell instant-slugs demonstrated, with astonishing results, buy a Thai exchange student at our club some years ago. A standard 12-ga target load vaporized a fist-sized cobble with no trouble. He cautioned that it works well only with new shells. I few days later, I recall him spending the whole afternoon trying to clear the mess an instant-slug from a reload had made.
If I understood him correctly, the "slugs" were commonly used in Thailand because standard slugs were prohibited. The government would allow civilians ammo only for target work, birds and small game. If you wanted to go after pigs, you had few options other than the circumcision specials.