Not wanting to have another poster's thread hijacked, I started this one to discuss what others felt/believed/observed about enhancing and promoting bullet toughness. I am only discussing the castings here, not the A-Frames & Partitions & TTSXs--as fine as they are.
For me, a harvester of varmints and thin-skinned game under 300# (usually A LOT under 300#), the Bruce B Soft Point has a lot going for it when driven between 1200 and 1800 FPS. I do hedge my bets here--I put these up in flatnose bullet designs that have something of a track record already as game harvesters--Lyman #311041, #375449 or its RCBS clone, Lee 45 rifle 405 grainer. I have shot one animal of fair size (a coyote) at 115 yards with the 30/30 and BBSPs, a bang-flop that traversed the carcass completely at an oblique angle from back of left ribcage entry, about 1/2 inch diameter, to exit at point of right shoulder with 1-1/2" stellate aspect. Muzzle velocity was 1800 FPS or thereabouts. I have 20 of these on hand, and they will join me on at least one day's deer hunt this Fall.
But what enhances "toughness"? Pure lead in patched roundballs kills in a manner out of proportion to its weight and ballistic coefficient, and I surmise that it does this because it generally does not shatter against tougher animated media as was seen in the cape buffalo examples with hardened alloy bullets. It does rivet over a bit, and essentially what I try to achieve with the BBSP is to drive a pure lead nose into and through an animal with a hardened shank to convey inertia to an expanding/riveting nose portion. Bruce did not say this per se, but I think a similar effect was what he had in mind for his bi-metal fusings.