How much pewter is too much pewter?

[AlexAkai]

Looking through the calculator for BHN 20 rifle bullets, 2 pounds of pewter to 4 pounds range scrap will get me there. My concern is will the bullets be to brittle or any other issues I need to be aware of?

I will be powder coating the rounds and gas checking them, under a load of 17.5 grains of H4198 in an AR 1/8 twist with a 16" barrel.

The first two I hit with a hammer once, the last one I pounded on several times to see if it would shatter.

These were water quenched and will be water quenched after powder coating.

Notice the odd coloration of gray and bright silver?

[turtlezx]

wow gonna be a lot of coments coming on this 1 2 to 1 tin

[sureYnot]

I'm currently mid-adventure with my AR 1:7 twist. So far I get accuracy with 18grns IMR4895 under a 55grn boolit... But it doesn't load the next round. In the next couple days I'm testing some other loads. Hopeful that I can help you out.

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Edit: just WW and powder coated

[jsizemore]

Water quenching does nothing to further harden a lead/tin alloy.

Beyond 10% tin stands the chance that you'll plate tin to the bore of your gun. It's heck to get out of a mold, imagine in a barrel.

[sureYnot]

Truth. Needs antimony and/or arsenic.

Water quenching does nothing to further harden a lead/tin alloy.

Beyond 10% tin stands the chance that you'll plate tin to the bore of your gun. It's heck to get out of a mold, imagine in a barrel.

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[GhostHawk]

Clip on wheel weights blended half and half with range scrap or soft lead. 1-2% tin.
So if I had 50 lbs of each a pound to a pound and a half of tin is what I would aim for.

YMMV.

[retread]

From the best(IMHO) source for casting: From Ingot to Target:
A Cast Bullet Guide for Handgunners
Glen E. Fryxell and Robert L. Applegate

This will explain the basics.


Metallurgy of the Cast Bullet
Lead-tin (Pb-Sn) - Which metals do we add to lead to make better bullet metal and why? The first and most obvious need here is to make the alloy harder, but there are other factors that play into this answer as well. Historically, tin was used because it was readily available in pure form, mixed easily with molten lead and contributed desirable properties to both the molten and solidified alloy (castability and hardness, respectively). Tin also increases the hardness of the alloy but does not interfere with the malleability of lead (a key point that we‘ll return to). Tin lowers the viscosity and surface tension of the molten alloy, allowing it to fill out the mould more effectively, resulting in a higher quality bullet. Tin is limited in its ability to harden lead, achieving a maximum hardness of about 16 BHN at 40% tin. These binary lead-tin alloys undergo slight to moderate age softening upon storage (1-2 BHN units), with the harder alloys undergoing more of a change than the softer alloys. The hardness of a binary lead-tin alloy generally stabilizes after about 2-3 weeks. Heat treating binary lead-tin alloys does not provide any change in hardness. At typical lead pot temperatures, lead and tin are infinitely miscible with one another, at the eutectic temperature (361o F) tin is still soluble to the tune of 19%, but at room temperature tin is still soluble in lead at the 2% level, meaning that as the bullet cools down there is significant precipitation of a tin-rich solid solution in the form of granules and needles in a matrix of lead-rich solid solution.
It is important to recognize that tin is well-mixed in the matrix and it hardens lead by making the matrix itself harder.
Lead-antimony (Pb-Sb) - Antimony on the other hand hardens lead alloys much more efficiently, with only 1% antimony producing a BHN of 10 while it takes 5% tin to do the same, and it takes only 8% antimony to achieve a BHN of 16, as compared to 40% tin. The name “antimonial lead” refers to binary lead alloys with 1-6% antimony, with the higher antimony alloys (i.e. those with >1% antimony) commonly being called “hard lead” in industry. While antimony increases the hardness of lead, it does so by
BHN of Binary Lead-Tin A510152001020304050BHNPercent Tin
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impairing its malleability. At typical lead-pot temperatures (ca. 700o F), antimony is only moderately soluble in lead alloys, and as the temperature drops, the solubility of antimony is markedly lower than that of tin. At the eutectic temperature for a binary lead-antimony alloy (484o F), only 3.5% antimony is soluble (note that this is 123o F hotter than of the tin eutectic temperature, but the antimony solubility is less than 1/5 that of tin). At room temperature the equilibrium solubility of antimony in lead is only 0.44%. The precipitated antimony appears as small rods, at the grain boundaries and within the grains themselves. Electron micrographs of lead-antimony alloys clearly show discrete particles of antimony surrounded by a matrix of lead-rich solid solution. In contrast to lead-tin alloys, lead-antimony alloys age harden, sometimes as much as 50% or more. When these alloys are air-cooled, some antimony is retained in the lead-rich matrix and as a result these alloys age-harden as this antimony continues to slowly precipitate. This usually takes 10-20 days to achieve full effect.
It is important to recognize the antimony hardens lead alloys by a fundamentally different mechanism than does tin. Antimony hardens the alloy by precipitation of a separate crystalline antimony phase, which reinforces the
squishy plastic lead phase that’s in between the hard antimony crystals. These alloys tend to be brittle because the plastic (squishy) lead phase gets its hardness from the reinforcing hard antimony rods. As the matrix gets deformed the brittle antimony rods shear off and the soft metal fails. In the case of the lead-tin alloys, the tin is more uniformly distributed through out the matrix, making the matrix itself harder, so plastic deformation of the alloy is more uniform and progressive, not the slip/shear of lead-antimony alloys.
BHN of Binary Lead-Antimony Alloys46810121416012345678BHNPercent Antimony
Multi-component alloys - Tin still improves castability by lowering viscosity and surface tension. Antimony hardens the alloy via precipitation. The tin also helps to alleviate brittleness by combining with the antimony to form an intermetallic adduct thereby improving the solubility, maintaining the hardness. Antimony also helps to reduce shrinkage as the alloy cools. The harder the alloy, the less it shrinks (lead shrinks 1.13%, linotype shrinks 0.65%). In molten lead alloys, tin and antimony react with one another to form an intermetallic compound (shorthand is “SbSn” to show the adduct between antimony, Sb, and tin, Sn). This does a number of things. First of all, SbSn is more soluble in lead than is Sb. In addition, both free Sb and Sn are soluble in SbSn, as is Pb, meaning that the formation of this phase serves to enhance the mixing of the alloy and limit phase segregation and precipitation. When Sb and Sn are present in roughly equal amounts, the alloy behaves as though it’s a pseudobinary system of SbSn in Pb. Electron micrographs of 94% Pb, 3% Sb and 3% Sn (an excellent bullet metal, very similar to WW alloys with 2% added tin) shows globular grains of lead rich solid solution, with an interdendritic
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pseudobinary eutectic of SnSb phase (for example see: the Metals Handbook: Volume 7, Atlas of Microstructures of Industrial Alloys, page 304). Similar electron micrographs of linotype alloys show very thin dendrites of lead-rich solid solution, surrounded by a matrix of SnSb intermetallic phase, with much precipitated antimony rich solid solution (this precipitated phase is why linotype bullets are so brittle and tend to shear upon impact).
How these alloys are hardened depends on the composition. The malleability of lead-tin-antimony tertiary alloys depends heavily on composition, particularly on the tin/antimony ratio. When the concentrations of tin and antimony are equal, the alloy behaves as though it’s a binary system with “SnSb” as the diluents in the lead matrix. The phase behavior of SnSb is notably different than that of Sb -- both in terms of solubility and in terms of crystal morphology. Sb is highly crystalline and only soluble in Pb to the tune of 0.44% at room temperature. SnSb appears to be significantly more soluble in Pb and based on electron micrographs of chemically etched samples, significantly more amorphous. As mentioned before, the SnSb phase serves as a mixing agent, serving to help dissolve excess Sb (or Sn for that matter), and having greater solubility in the Pb matrix. This enhanced mixing, along with the reduced crystallinity means that the lead alloys with a 1:1 ratio of tin to antimony behave somewhat like simple binary lead-tin alloys, only harder (this is why Lyman #2 is 90% Pb, 5% Sb, 5% Sn). Hold this thought…
As the concentration of antimony increases over that of tin, at first the SnSb phase serves to dissolve the small amount of excess Sb. At higher Sb concentrations however the SnSb phase becomes saturated and a separate antimony phase begins to precipitate. At this point, the alloy begins to take on some of the brittleness properties of the binary lead-antimony alloys. As the antimony concentration increases, this brittleness becomes more pronounced. So those tertiary alloys which have 2 or 3 times as much antimony as tin (e.g. linotype, 12% Sb, 4% Sn) tend to be more brittle than those alloys of similar hardness with similar Sb and Sn levels. OK, here’s a subtle point, WW alloy (3% antimony, 0.3% tin) can fall prey to this issue as well, although not as severely since it’s not as hard. But by adding tin and making the alloy slightly harder, the alloy also becomes less brittle and more malleable due to the formation of SnSb and the elimination of the precipitated Sb phase. Thus, WW alloy with approximately 2% added tin makes an excellent bullet metal with hardness suitable for a variety of applications, and it still can be made harder through heat treating or water quenching. This can also be made using Lyman #2 mixed with an equal amount of pure lead.