Even more good advice there.
As for hardness, you gotta have them a little harder than pure lead or you will likely get a bad case of leading in your barrel to the point where accuracy goes south pretty quickly. Were it me, I would mix your pure lead 50/50 with wheel weight material, or perhaps softer at 60/40 in this instance.
You're asking a lot of a cast bullet at these low velocities. One can't expect much expansion. Again, were it me and I was faced with your needs (I didn't realize it was such a big necessity to work up a deer killing load with barely-sonic velocities- my bad, I thought you were looking for a plinking load), I would also consider a hollow point design to help things along, or at the very least a big wide flat point (meplat) like that Lee Soup Can design.
I would also look into a heavy weight bullet, say 190-220 grains, cast soft, with a hollow point if I were going to seriously consider shooting a deer with 11-1200 fps loads. Still "quiet" and with a lot more kinetic energy. Going much faster than that, aside from being louder, you start getting into the realm of needing a gas checked bullet which I don't know if you want to go that route.
This hobby is simple as heck on the one hand, and devilishly complicated on the other.
