Zinc equivalent for Manganese Bronze Alloy

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I am currently producing a manganese bronze alloy C86500 (Copper base) and using the formula below I am trying to obtain a zinc equivalent between 43 and 45.

Here is the formula Zn Equivalent = (Al*6)+(Ni*-1.3)+(Mn*.5)+(Sn*2)+(Fe*.9)+ Zn

My question is that I am looking for any documentation about his formula and what zinc equivalents should I be looking for in another Manganese Bronze alloy C86700 ?

Thank you