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#591837 02/10/21 07:16 AM
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Does anyone have a formula for calculating lead alloy bullet weight? For example, I have two .400” bullets each 0.900” long. One is pure lead and weighs 278 grains. The other weighs 228 grains, and I’d like to figure out its likely lead alloy content.
Math was never my strong suit, so forgive me if the formula for solving this is easy.
Thank you math geniuses in advance


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You have to know what the other constituent metal was, otherwise all you can say is one is more dense than the other.

If, for example, one component was tin, and for all intents and purposes the only other component was lead, then you could figure out the percentage of each in the alloy pretty easily. Because we know the density of tin, and we know the density of lead.

It’s what is called a weighted average.

But it gets considerably harder, if there are multiple alloying components.


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ClapperZapper is correct. It is very simple to calculate the volume of your bullet, knowing how much it weighs when cast of pure lead. But there are so many alloys used as bullet metal, that you would need to have an assay done to know the exact composition of your unknown alloy.

But you may find what you are looking for here:

http://castboolits.gunloads.com/showthread.php?105952-Lead-alloy-calculators


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yes, it is easily done IF it is just lead and tin. But in all likelihood you probably have antimony in there too and that means you have 3 unknowns and only two independent equations. In other words, "What ClapperZapper said".


I calculate lead-tin ratios for casting all the time and have a spreadsheet set up for it to make it simpler, but it's only good on PB/SN alloys.

Last edited by BrentD; 02/10/21 11:44 AM.

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For what it’s worth, with three variables, especially knowing that antimony never gets whst? above 6%? You could actually do the calculation using antimony as a fixed 4%, and could very easily come within one or 2% on the actual alloy if you knew that the alloy was only lead and tin.

Certain variables dominate the equation.In other words, in terms of their overall effect within a weighted average, they behave as though they are fixed. Or at least contribute so little, that you can treat them as though they are fixed.


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Calculations assume perfect casting. If that light bullet can be sacrificed, it may have a void in it.

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Probably obviously harder or softer if the alloys are so different as well


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The easy way, take it to a friend who buys and sells gold.
Ask him to run it through his mass spec
Then you will know



Mike

Last edited by skeettx; 02/12/21 02:02 PM.
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Originally Posted by ClapperZapper
You have to know what the other constituent metal was, otherwise all you can say is one is more dense than the other.

If, for example, one component was tin, and for all intents and purposes the only other component was lead, then you could figure out the percentage of each in the alloy pretty easily. Because we know the density of tin, and we know the density of lead.

It’s what is called a weighted average.

But it gets considerably harder, if there are multiple alloying components.

Thank you. I am going to have to assume that tin alone was used as the alloying metal with the lead


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Originally Posted by keith
ClapperZapper is correct. It is very simple to calculate the volume of your bullet, knowing how much it weighs when cast of pure lead. But there are so many alloys used as bullet metal, that you would need to have an assay done to know the exact composition of your unknown alloy.

But you may find what you are looking for here:

http://castboolits.gunloads.com/showthread.php?105952-Lead-alloy-calculators
Thanks, Keith. That lead me down a deep and dark rabbit hole, but it was filled with a lot of interesting information. Surely useful to someone better at math than I...


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