Half the Antimony and 1/4 the tin? 2.5% Sb and 2% Sn.
Lead gives BHN of 5
2.5% Antimony adds about 2.2 BHN
2% Tin adds .6 BHN
For a hardness of 7.8 BHN
At that low level of tin, I can not make the mold fill properly. Additional tin aids wetting properties thus mold fill.
My goal is duplication of Lyman #2 with possibly a bit additional tin.
I have 200 lb melted and formed into ingots. It looks like I might have enough components for another 200 lbs. But then I have to remelt it all and blend the batches for a uniform lot.
Either your calculations are off or my Bhn tester(Cabine Tree) and rifle performance are. I'm getting 10-12 Bhn with most of my batches. Using an alloy spreadsheet calculator on another site, I mix range lead(mostly full jacket pistol with some cast bullets mixed in that I've had tested at 1.4%Sb), pewter and Linotype or know alloy babbitt. Probably 90% of my alloys run under 1.5% Sn, and under 2% Sb. If you get the fit right hard isn't needed. If you get it wrong, sometimes hard makes it worse because the bullet won't obturate as needed. To me, hard is anything over 15
Edit to add
I checked that spreadsheet and the example you gave as 2%Sn, 2.5%Sb shows a Bhn of 11-12, not 7.8
