This. I've read 00 buck shot may provide more damage/success but I would think a slug would certainly do it. 12 Gauge slug, largest size you can get through the barrel. I believe it depends on smooth bore barrel or rifled etc. None the less I have considered this method and believe it to be be a very reasonable choice in regards to avoiding personal suffering. In belief that others may be reading this. Always go 12 gauge, and do not use bird shot.