At 1400 FPS I wouldn't cast those bullets Too hard. A lead bullet cast too hard will not bump up to give a good seal in the throat or bore nor will it give any expansion on game, but will act like a full metal jacketed bullet. I would think a Brinell hardness of around 15 would be plenty if not more than enough.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra