If you air cooled them, they are about as soft as they are likely to get. If I've got it right, and there are folks who know a lot more than me, the brittleness is caused by the presence of antimony in the alloy. You can cut WW with lead to get the antimony content down, but if you want cast bullets to expand at .45 ACP velocities, you are going to have to go to pure lead or lead with a small amount of tin added, say 30-1.