This topic came up a couple of times in the last few years. I mentioned previously: I saw a cut, or circumcised, shell instant-slugs demonstrated, with astonishing results, buy a Thai exchange student 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 afternoon trying to clear the mess from an instant-slug made from a reload. The crimp had opened just before the choke and the partial hull and wad were stuck in the barrel.
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.