How does the alloy's composition effect diameter & filll rate

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Last Post 27 March 2021
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Wm Cook posted this 20 March 2021

How does alloy's composition effect bullet diameter and fill rate?

Example: A single cavity iron mold is cut with a body (drive bands, bearing surface) diameter that measures .3100 +/- .000.

How does the body (drive bands, bearing surface) diameter of the bullet change when using different alloys (Example: 20/1 versus #2 Lyman versus Linotype (94Pb, 12Sb, 4% Sn)).

To eliminate operator error assume it's you casting with a proven mold using your techniques and using your practices.

So the question is how does the diameter and fill rate change when using different alloys.

Thanks to folks like Larry, Rick, Bud and others for help getting me squared up as I move into cast accuracy. Bill.

A “Measured Response” is as effective as tongue lashing a stuck door.

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pisco posted this 20 March 2021

There is a formula and the more anatomy and tin the bigger the projectile measure I’ll find the book it’s in

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Wm Cook posted this 20 March 2021

So there’s a mathematical equation that takes the percentage of lead, tin, antimony and can calculate the amount of shrinkage of the Bullet? That’s amazing. I had thought it was entirely a learned experience. Like maybe Linotype would shrink x and pure lead would shrink y.

A “Measured Response” is as effective as tongue lashing a stuck door.

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CBA Member

RicinYakima posted this 20 March 2021

From RCBS Cast Bullet Manual number 1:

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RicinYakima posted this 20 March 2021

Recommended manual, but out of print since 1986. Lots of used ones around, but not cheap.

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Wm Cook posted this 21 March 2021

Thanks for the directions. I have the manual and there were some good articles in the forward section. So as far as dimensionally speaking it seems nearly inconsequential whether it’s the #2 running ~ 16 bhn that I’m using or the Linotype I can get from Rotometal that I think runs about 22 bhn. Dimension change looks to be in the neighborhood of about 3 tenths of a thousands larger. My guess is that fill out is going to be the same with the tin amount being used. I don’t think the larger amount of antimony will effect fill out but that last is just a guess. Thanks, Bill.

A “Measured Response” is as effective as tongue lashing a stuck door.

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CBA Member

Bud Hyett posted this 22 March 2021

I concur with all the above. I'll add that this becomes as much art as science. Working with known alloys can set a baseline and is a good beginning. You'll soon discover there are many factors. E.g., individual rifle chamber and barrel, individual mold dimensions, ambient temperature at the range, shooter fatigue, etc., can have impact either testing or in a match.

As an extreme example; when final testing a load, I take a BSA Martini to the range with a known lot of ammo to see that I am shooting well. If it groups well, I know I am pulling the trigger correctly and one more factor is mollified.

Keep records of your testing, both good and bad targets. When done, add a note to the target face of any item you noticed. Call your shots, the flyer may be you and it may not, add this record. I think the quest for accuracy is not so much getting a single small group, but to eliminate the flyer, or several, while shrinking the group size.

I'm again building a database using the attributes of the CBA Technical Sheet to record my testing. These are the pertinent attributes affecting accuracy in my experience. Overkill, I think not. You can do the same recordkeeping using EXCEL Spreadsheets

Casting bullets has brought to me the truth of this saying, "Good judgement comes from experience and experience comes from bad judgement."

Welcome to the fascinating world of the Dedicated Amateur Ballistics Researcher And Theoretician.

Farm boy from Illinois, living in the magical Pacific Northwest

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Eutectic posted this 24 March 2021

Shrinkage after casting is greatest with lead and least with linotype, intermediate alloys come between lead and linotype.

Lead - 1.1%
3% tin, 97%lead - 1.0%
4% tin, 96% lead - 0.93%
5% tin, 95% lead - 0.925%
5% tin, 5% antimony, 90% lead - 0.9%
2% tin, 6% antimony, 92% lead – 0.7%   Commercial cast bullets
4% tin, 12% antimony, 84% lead – 0.65%   Linotype

Shrinkage is variable, depending on the temperature of the mold and alloy. Therefore, the diameter and weight of the bullet will vary with both the alloy and casting conditions.

There is another consideration, the size of the mold cavity. Your mold expands with temperature. There is a difference in the mold from cool casting (bright bullets) and hot casting (frosted bullets). the difference is greatest with an aluminum mold, but is there with all mold materials. This is a % difference so diameter and length differences are greatest with large/long bullets.

Steve