In my experience, that 30-1 alloy should NOT be that hard. Tin just does not harden pure lead all that much. Where did you get that 9.1 figure for the 30-1 alloy? I would say that the reading you got for the 30-1 from the lee tester was correct.
Tin does 2 things for lead when it's the ONLY other metal in pure lead. It makes the lead melt at lower temps, allows it to be more liquid so it fills molds better, and toughens the metal. Okay that's 3 things!
But it does not harden it much.
Now if there's antimony in the lead, tin combines with the antimony to really harden it. In fact the tin HAS to be included, or the antimony won't go into solution with the lead, it exists as separate crystals surrounded by pure lead. There's a ratio, that I can't remember right now, that has to be maintained, or the antimony won't mix with the lead.