# Parts and percentages

When I got into bullet casting, I noticed right off that there was confusion over parts and percentages.  People tell you that 20 parts lead to one part tin equals 95% and 5%, but when you start adding your “parts” you put in 20 parts this and one part that, and you realize that you now have 21 parts, which isn’t 95:5.  It’s actually 1/21, which is more like 95.3% and 4.7%.  Not a big difference, and not enough to really matter in this case, but when mixing several ingredients, you can end up farther off.  If you use this oft repeated “method” of calculating for things that really do matter, you’re in trouble.

Anyway, I wanted Lyman #2, and Lyman states the actual percentages.  I use other alloys too, and several sources of metal, so I made up this alloy calculator.

I think my assumptions are right…

Alloy Calculator.xls (26.5 KB)

You can fiddle with the composition of your various metal sources, plug in the number of parts in each, and it gives you the makeup of your final alloy in percentages.  So I can make #2 alloy from wheelweights, pure tin and 70:30 antimonial lead, or from pure lead, tin, and 70:30, etc. and in theory get a pretty consistent product without having to do much calculating.

## 2 thoughts on “Parts and percentages”

1. Having never done it, is that by volume or weight?