I cast all of my revolver hunting bullets for deer. I do not have a hardness tester. I have lots of wheel weight lead that I sweeten up with a little extra Tin. I suspect that my bullets are softer than 20, as I recovered one of my 310 grain 44 Magnum bullets from a deer showing quite a bit of expansion. I was totally shocked that the bullet stayed in the deer.
My main consideration is that the bullets do not lead the barrel.

I prefer a broad side shot through the ribs behind the shoulders to minimize meat damage on White Tail Deer. Where I hunt I normally do not need to drop the deer in its tracks to prevent it from running down hill into a canyon. With a broadside rib shot I doubt I will ever get much expansion from my cast bullets.

My brother hunts with the 44 Magnum. I cast and load his ammunition. His recovered 310 grain bullet was in the shoulder.

My revolver is a 480 Ruger. I have never had a deer go over 40 yards from where I shot it on a broadside rib shot with my cast bullets.

My advice would be to keep the bullets hard enough that they do not lead the barrel. If you get expansion on a shoulder shot, consider it a bonus, and not a requirement. Also get a Gas Check bullet mold with at least a 70% Meplat. Big Flat Nose Bullets hit hard.

I got an old Lyman Lube Sizer in a trade a while back. PM me if interested.

Bob R