Trying to craft bismuth bronze in a small vessel and percentages don't seem to be working or there is a mechanic I am not aware of.
6 small chunks Cassiterite for 60 mb Tin 30%,4 small chunks bismuth for 40 mb 20%, 10 small chunks Tetrahedrite for 100mb Copper 50% is producing unknown metal. I check in game doc and 2 wiki's and seem to agree with the percentages.

From the Field Guide

Requirements:

• 20 - 30 % : Zinc
• 50 - 65 % : Copper
• 10 - 20 % : Bismuth

Zinc/Sphalerite is not Tin/Cassiterite.