Welcome to the Brotherhood of the Silver stream !!!!!!
Lee molds are configured with Lyman#2 alloy .
Your alloy as stated contains less alloy than #2 & I`m suprised ya got 15+ bhn from it WDing , but it`s not written in stone what alloy mix WW are either !!!!
My Lee 158rnfp drops at 162 with WW & 170 with 50/50 WW & stikons.
I mainly use isotope containers now , nice steady supply & most containers run 10.5 bhn , some harder.
I seperate Stik ons from Clip ons as I look for the Zn & Fe , They make good tradin fodder to the Muzzle loading & Cap& ball revolver shooters.
Zinc makes lead hold itself tite & won`t fillout a mold correctly no matter how hot ya get the melt & mold !!!
Here`s a pic of the Zn weights I`ve run into but no means a complete compilation !!!