Here is some basic info on the common metals of bullet casting that could be beneficial to new casters.
Lead (Pb) melts at 621.3 F and has a BHN of 5. Lead alloys with some metals very well, not so easily with other metals. Lead is a very heavy, ductile or if you prefer malleable metal. Its weight is what carries the bullets momentum to the target and being malleable is what allows it to conform to the bores dimensions (obturation) and seal off the rising gas pressure.
Unlike most types of steel alloy’s that become more brittle when heat treated, lead alloy can be heat treated and made harder without adding any brittleness. Unlike most types of steel alloy’s (or your brass cartridge cases) that become harder and brittle when worked, lead when worked becomes softer. Heat treated lead, unlike steel, does NOT surface harden but achieves the same BHN all the way through.
Perhaps the single most significant error in all the bullet casting literature is the misconception that lead-tin-antimony alloy melts will gravity segregate.
Lead conducts heat slowly and contrary to the belief of some, lead does not melt from the base of plain base bullets when fired causing leading. If it could why don’t paper and plastic wads burn in shotgun shells? The millisecond the bullet is subjected to this heat simply could not melt lead. Pressure forcing the bullet against the sides of the bore could and far more likely than this is a bullet too hard or an under sized bullet
allowing gas leakage down the sides of the bullet. This has the same effect as an acetylene torch cutting steel and leading would begin on the trailing edge of the rifling.
Molten lead alloy exposed to air soon oxidizes (this is NOT gravity separation). The chemistry of tin and antimony dictates that they oxidize at a higher rate, which accounts for their gradual depletion from the melt. The scum that forms on the surface of the melt is a mixture of metal oxides, not tin or tin oxide only. Fluxing returns much of the oxidized metal to the melt. Oxidation occurs only at the surface of the melt and in the flow stream from bottom pour pots. Tin helps reduce, not eliminate oxidation up to a max of 750 degrees. The bottom line, oxidation occurs wherever, whenever the molten alloy is in contact with air and thus the need for fluxing.
Antimony (Sb) melts at 1167 degrees F. It is the most common metal used to strengthen/harden lead alloys for bullet casters and for numerous applications in the metals industry. It is an extremely brittle metal but has unique characteristics in a lead alloy in addition to its basic hardening, such as the ability to heat treat a lead alloy bringing the final hardness up far more than what the percentage of antimony would suggest. Alloys such as monotype (19% Sb) and stereotype (23% Sb) are so brittle that bullets cast of them can actually break in two by simply chambering a round or dropping it on the floor. Antimony is a valuable part of the bullet casters alloy but too much of a good thing is clearly not a good thing. The type metals, linotype, monotype and stereotype, if you can still find them, are valuable to the bullet caster for their antimony and tin content when blending (alloying) with other lead alloys.
Tin (Sn) Tin melts at 449 degrees and alloys very easily with lead. Tin was used for many years as the hardening agent in lead. In the years of large caliber, big bore black powder cartridges the minimal hardening effects of tin was sufficient. With the advent of smokeless powders and much higher pressures and velocities of the smokeless powders tin’s limited hardening/strengthening effect on lead left alloys too soft for many cartridges.
Lead/tin alloy’s age soften and the higher the percentage of tin the faster the age softening. Tin is a very valuable addition to the bullet casters alloy. The true value of tin for today’s bullet caster is that it reduces the surface tension of the melt. It does this by inhibiting the oxidation of the metal entering the mold and enabling a more complete fill-out of the molds intricate details. NOTE: It is not only the surface of the melt in the pot subject to oxidation, the stream of alloy from a bottom pour pot or casting ladle is also in contact with oxygen and this is where tin has it's largest benefit in reducing oxidation and aiding better mold fill-out, from the spigot to inside the mold. Tin does add some hardening/strengthening to lead alloys but at the percentages in most bullet alloys it is minimal. Tin provides dross protection up to about 750 degrees and also improves castability. Casting temperatures with alloys containing tin should be held to about 700 degrees so that tin’s ability to reduce dross won’t be lost. Above 750 degrees tin itself oxidizes much more rapidly. Maximum hardness of lead/tin alloys is 17 BHN at 63% tin and 37% lead commonly known as 60/40 solder.
Arsenic (As) Melting point, 1,503 degrees F. Arsenic is a grain refiner very beneficial in heat treating Pb/Sb alloys and only a trace is required (¼ to ½ of 1%), adding more than this will do nothing to further harden the alloy. Arsenic in itself does little to harden the alloy; its value is as a grain refiner in heat treating (or quenching from the mold in Pb/Sb alloys. Arsenic is of coarse very toxic but at the percentage in and temperature of bullet alloys the risk is nearly non-existent. However, the bullet caster should never attempt to alloy elemental arsenic into his alloy (if he could even get it). Arsenic in combination with antimony, improves the strength. In the as cast condition arsenic raises the hardness about 1 or 2 BHN. Arsenic’s true value is in heat treating lead/antimony alloys. With a trace of arsenic a much higher BHN can be achieved while using a much smaller percentage of very brittle antimony.
Lead (Pb) melts at 621.3 F and has a BHN of 5. Lead alloys with some metals very well, not so easily with other metals. Lead is a very heavy, ductile or if you prefer malleable metal. Its weight is what carries the bullets momentum to the target and being malleable is what allows it to conform to the bores dimensions (obturation) and seal off the rising gas pressure.
Unlike most types of steel alloy’s that become more brittle when heat treated, lead alloy can be heat treated and made harder without adding any brittleness. Unlike most types of steel alloy’s (or your brass cartridge cases) that become harder and brittle when worked, lead when worked becomes softer. Heat treated lead, unlike steel, does NOT surface harden but achieves the same BHN all the way through.
Perhaps the single most significant error in all the bullet casting literature is the misconception that lead-tin-antimony alloy melts will gravity segregate.
Lead conducts heat slowly and contrary to the belief of some, lead does not melt from the base of plain base bullets when fired causing leading. If it could why don’t paper and plastic wads burn in shotgun shells? The millisecond the bullet is subjected to this heat simply could not melt lead. Pressure forcing the bullet against the sides of the bore could and far more likely than this is a bullet too hard or an under sized bullet
allowing gas leakage down the sides of the bullet. This has the same effect as an acetylene torch cutting steel and leading would begin on the trailing edge of the rifling.
Molten lead alloy exposed to air soon oxidizes (this is NOT gravity separation). The chemistry of tin and antimony dictates that they oxidize at a higher rate, which accounts for their gradual depletion from the melt. The scum that forms on the surface of the melt is a mixture of metal oxides, not tin or tin oxide only. Fluxing returns much of the oxidized metal to the melt. Oxidation occurs only at the surface of the melt and in the flow stream from bottom pour pots. Tin helps reduce, not eliminate oxidation up to a max of 750 degrees. The bottom line, oxidation occurs wherever, whenever the molten alloy is in contact with air and thus the need for fluxing.
Antimony (Sb) melts at 1167 degrees F. It is the most common metal used to strengthen/harden lead alloys for bullet casters and for numerous applications in the metals industry. It is an extremely brittle metal but has unique characteristics in a lead alloy in addition to its basic hardening, such as the ability to heat treat a lead alloy bringing the final hardness up far more than what the percentage of antimony would suggest. Alloys such as monotype (19% Sb) and stereotype (23% Sb) are so brittle that bullets cast of them can actually break in two by simply chambering a round or dropping it on the floor. Antimony is a valuable part of the bullet casters alloy but too much of a good thing is clearly not a good thing. The type metals, linotype, monotype and stereotype, if you can still find them, are valuable to the bullet caster for their antimony and tin content when blending (alloying) with other lead alloys.
Tin (Sn) Tin melts at 449 degrees and alloys very easily with lead. Tin was used for many years as the hardening agent in lead. In the years of large caliber, big bore black powder cartridges the minimal hardening effects of tin was sufficient. With the advent of smokeless powders and much higher pressures and velocities of the smokeless powders tin’s limited hardening/strengthening effect on lead left alloys too soft for many cartridges.
Lead/tin alloy’s age soften and the higher the percentage of tin the faster the age softening. Tin is a very valuable addition to the bullet casters alloy. The true value of tin for today’s bullet caster is that it reduces the surface tension of the melt. It does this by inhibiting the oxidation of the metal entering the mold and enabling a more complete fill-out of the molds intricate details. NOTE: It is not only the surface of the melt in the pot subject to oxidation, the stream of alloy from a bottom pour pot or casting ladle is also in contact with oxygen and this is where tin has it's largest benefit in reducing oxidation and aiding better mold fill-out, from the spigot to inside the mold. Tin does add some hardening/strengthening to lead alloys but at the percentages in most bullet alloys it is minimal. Tin provides dross protection up to about 750 degrees and also improves castability. Casting temperatures with alloys containing tin should be held to about 700 degrees so that tin’s ability to reduce dross won’t be lost. Above 750 degrees tin itself oxidizes much more rapidly. Maximum hardness of lead/tin alloys is 17 BHN at 63% tin and 37% lead commonly known as 60/40 solder.
Arsenic (As) Melting point, 1,503 degrees F. Arsenic is a grain refiner very beneficial in heat treating Pb/Sb alloys and only a trace is required (¼ to ½ of 1%), adding more than this will do nothing to further harden the alloy. Arsenic in itself does little to harden the alloy; its value is as a grain refiner in heat treating (or quenching from the mold in Pb/Sb alloys. Arsenic is of coarse very toxic but at the percentage in and temperature of bullet alloys the risk is nearly non-existent. However, the bullet caster should never attempt to alloy elemental arsenic into his alloy (if he could even get it). Arsenic in combination with antimony, improves the strength. In the as cast condition arsenic raises the hardness about 1 or 2 BHN. Arsenic’s true value is in heat treating lead/antimony alloys. With a trace of arsenic a much higher BHN can be achieved while using a much smaller percentage of very brittle antimony.
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