HI Dan as i recall an artical i saw a good wail back the guy that made that mold did so for a cast bullet that was for medal pearsing, the bullet was to be cast out of lyno type.that was in one of the old layman hand books. you may want to check this out but as i rember thats what i read
Like Bob, the story I heard for the lyman 358093 & 429303 was that law enforcement in the 20's and 30's wanted a bullet that would go through a car door and still be lethal when it hit the people inside. Lyman was recommending these bullets be cast very hard.
But now that the subject of 358093 & 429303 has come up <grin>. I have an extra two cavity 38093 mould in very good condition (as in mint) that I'd be willing to swap for a 429303 in good useable condition. My email is in my profile if anyone is interested. BTW, the mould is for trade, not for sale.