joeb33050
09-02-2008, 12:17 PM
MOLD AREA, BULLET WEIGHT AND CASTING SPEED
This article is about maximizing "good bullets per hour" of casting time; why some molds slow us down when casting and suggestions from casters about how to fix the problems that slow us down.
I think that there are only two things we can vary in bullet casting, the temperature of the pot and time. Temperature is easy, but time has several components.
Time the spout is in contact with the sprue plate or is keeping a molten puddle of alloy on the sprue plate.
Time between moving the mold from the spout and opening the sprue plate.
Time between removing the bullet and closing the sprue plate and starting the next pour.
Time has some value to us, even to old retired guys like me. I'd like to cast good bullets faster.
The "fixes", below, are necessary because there's an imbalance between the alloy freezing temperature and the mold dimensions.
If the mold is too small, it has to be cooled down.
If the mold is too big, it has to be heated up.
Reports from well-instrumented bullet casters state that during the casting process, molds cool off more than I'd ever expected, from ~500-550F to ~250-350F between solidification and re-pouring. Molds are excellent heat dispersers. Heat dispersion with molds of a given material, iron or brass or aluminum, in still air, at room temperature is a function of the total heat in the mold and the surface area of the mold.
If the mold is going to cast a great big bullet, the mold needs to be big.
If the mold is going to cast a small bullet, the mold needs to be small.
Optimum mold size, for maximum casting speed, is a function of bullet weight, and maybe dimension ratios; but certainly of bullet weight.
Molds are classified as "hot", "ideal" or "cold" here.
"Hot" molds require cooling off between pours, a slow pace of casting that results in fewer good bullets being cast per hour than with an "ideal" mold. An example is my Ohaus 45-405 single cavity (SC) mold that casts 45 caliber 433 grain bullets, but not many good ones per hour.
"Ideal" molds will cast good bullets as fast as you can go through the casting steps, with no waiting time between pour and open-the-mold. These molds are just right; normal, unhurried and un-slowed cycling through the casting steps gives us good bullets, fast.
"Cold" molds require a lot of mold heat-up time and quick casting. If you stop for a bit you get wrinkled bullets. These molds are too cold. An example is my custom #78-185, a 185 grain 30 caliber SC mold that produces wonderful bullets, slowly.
ALLOY EFFECT
Different alloys of lead (Pb), tin (Sn), and/or antimony (Sb) melt at different temperatures. Most of these alloys go through a slushy stage between completely solid and completely liquid. The metals; lead, tin and antimony do not go through a slushy stage. Some alloys have a sharp solid-liquid temperature, with no slushy stage. These are called "Eutectic" alloys.
Here is a table of temperatures where the metals or alloys are solid, slushy (if they are slushy), and liquid. All temperatures in degrees F
Metal or alloy Solid Slushy Liquid Note
38.1% Pb/61.9% Sn 361.4 Not 361.4 Eutectic, "63/37"
Tin 449 Not 449
Linotype 463 Not 463 Eutectic
91% Pb/2% Sn/7% Sb 463 <<Slushy between>> 525
88.8% Pb/11.2% Sb 484.2 Not 484.2 Eutectic
94%Pb/6%Sb 486 <<Slushy between>> 550
90% Pb/ 10% Sb 486 <<Slushy between>> 500
95% Pb/ 5% Sn 522 <<Slushy between>> 597
97.5% Pb/ 2.5% Sn 608 <<Slushy between>> 617
Lead 621 Not 621
Antimony 1166 Not 1166
Source: The Art Of Bullet Casting, Jerry Gonicsburg On "ALLOYS FOR CAST BULLETS"
Note that the numbers given above may vary slightly by source. For example, CAST BULLETS by E.H. Harrison, page 16, has the eutectic lead/antimony alloy as 87.3% Pb/12.7% Sb rather than the 88.8% Pb/11.2% Sb above.
For a continuous although virtually incomprehensible graph of melting points of lead, tin, antimony alloys, see the Lyman CAST BULLET HANDBOOK, third edition, pg. 47.
The important things about this, to me, are that (1) lead, tin, antimony metals and alloys melt at widely varying temperatures, and (2) the melting temperature generally goes down as tin and/or antimony are added to lead.
"Cold" molds may operate OK when casting in linotype or other tin-and/or- antimony-rich alloys such as linotype; this because these alloys melt and solidify at lower temperatures than alloys with higher lead percentage, such as 25:1. An example is the RCBS 22 caliber 55 grain double cavity mold. Some casters report this mold as very cold, others, casting in linotype, report this mold as ideal.
BULLET SHAPE
Pistol bullet molds do not seem as sensitive to the "hot" characteristic as do longer rifle bullets. My guess is that bullet with shapes approaching spherical transmit less heat to the mold than do longer thinner bullets.
AGGRAVATION TOLERANCE
To some degree the "cold"-"ideal"-"hot" characteristic of a mold is a reflection of the aggravation tolerance of the caster. The more blasé casters are happy with molds that drive the more sensitive caster nuts.
MOLD WEIGHT
Many "cold" molds are relatively heavy. I find it easier, less tiring and faster to cast good bullets with a lighter mold; and I am enormously strong. Lighter is better.
MEASURING-THE "IDEAL" MOLD
I took a sample of molds, mine and molds belonging to others, only iron/steel molds. No Hoch molds because the geometry is so different from that of other Lyman or RCBS or NEI or Ohaus molds.
I did a lot of measuring and calculating and casting, and got comments from fellow casters. At the end, there was a pretty clear relationship between the surface area of the mold, (not including the sprue plate), and the nominal weight of the bullet/s. An EXCEL workbook containing all the data, "Mold areas and bullet weight", is in "ERRATA".
Here's how the measurements and calculation were made:
Measure the length, (parallel to the handles), width, (across the mold halves), and height of the mold; then calculate the surface area in square inches.
Divide the nominal bullet weight, (a double cavity 55 grain bullet mold has a nominal bullet weight of 110 grains), by the mold surface area and get "grains per square inch".
The Ohaus 45-405 mold had the largest number of grains of bullet weight per square inch of mold at 49.7 grains per square inch.
The Ohaus mold is "hot" because it has too much lead going into too small a mold.
The custom #78-185 mold had the smallest number of grains of bullet weight per square inch of mold at 15.6 grains per square inch and is too cold because it has too much surface area for the size of the bullet. This mold is "cold" because it has too little lead going into too big a mold.
Molds with between 20 and 40 grains of nominal bullet weight per square inch of mold surface area were "ideal".
FIXES
The perfect fix would be to have mold manufacturers vary mold dimensions to correspond with nominal bullet weight.
When casting with a given mold and alloy we can, and should, adjust the pot temperature to make casting good bullets as fast as possible. A "cold" mold wants the pot and alloy hotter; a "hot" mold wants the pot and alloy cooler. If the alloy is too cool for the mold/alloy combination the bullets will be wrinkled. If the alloy is too hot for the mold/alloy combination the sprue will take a long time to harden, bases will have those rough looking holes at the sprue and the bullets will tend to be frosted.
Allow enough time for the pot temperature to stabilize, experiment with different thermostat settings, and write down the settings and results. A thermometer is handy during this temperature adjustment.
Remember that at some temperature north of 800 degrees F the alloy and/or its constituents begin to oxidize very quickly.
"HOT" MOLD FIXES
(Water + molten lead = explosion. Be very careful with water anywhere near the lead pot.)
From "The Modern American Rifle" A. C. Gould, copyright 1891: "...Before commencing, place a dish of water near you, and a mallet or stick of wood; the first to plunge the mold into when it is growing too hot,"
Now A. C. is talking about a "hot" mold. And what he's doing is cooling the mold off so he can cast faster, so he can get more bullets per hour.
Dick Howes at the Old Colony Sportsman's Association advocated mold cooling by touching the mold bottom or sprue plate to a wet sponge or folded cloth. He was able to cast a lot of good bullets quickly using this method.
Lately, (2008), Bruce B. on the "Cast Boolits" forum has cast amazing quantities of bullets in short times using his adaptation of these cooling methods.
Cast with more than one mold and allow alternate molds to cool between pours.
Cool the mold in a stream of air from a fan.
Cool the mold on an aluminum plate. I've had good luck cooling the bottom of the mold on a flat aluminum plate, and on the bottom of my aluminum muffin pan/ingot mold.
If the mold has two cavities, pouring into just one cavity will reduce the mold temperature and may actually increase production of good bullets.
It has been suggested that replacing the sprue plate on a "hot" mold with a great big sprue plate will make the mold less "hot".
"COLD" MOLD FIXES
Cast a lot with a new "cold" mold. As the mold surfaces oxidize or blue the heat transfer rate seems to go down and the mold gets less "cold". A lot of use doesn't fix the problem, but does lessen it.
Using a mold-prep in or smoking the mold cavity/ies may make the mold less "cold". Some casters suggest using mold-prep on, or smoking, the outside-the bottom and sides of the mold, to make it less "cold" by slowing down heat transfer.
Heat the mold on an electrical hot plate or with a propane torch; or dip the mold in the pot of alloy. These actions may work best when done with varying frequencies, such as before each pour, every second pour, etc.
This article is about maximizing "good bullets per hour" of casting time; why some molds slow us down when casting and suggestions from casters about how to fix the problems that slow us down.
I think that there are only two things we can vary in bullet casting, the temperature of the pot and time. Temperature is easy, but time has several components.
Time the spout is in contact with the sprue plate or is keeping a molten puddle of alloy on the sprue plate.
Time between moving the mold from the spout and opening the sprue plate.
Time between removing the bullet and closing the sprue plate and starting the next pour.
Time has some value to us, even to old retired guys like me. I'd like to cast good bullets faster.
The "fixes", below, are necessary because there's an imbalance between the alloy freezing temperature and the mold dimensions.
If the mold is too small, it has to be cooled down.
If the mold is too big, it has to be heated up.
Reports from well-instrumented bullet casters state that during the casting process, molds cool off more than I'd ever expected, from ~500-550F to ~250-350F between solidification and re-pouring. Molds are excellent heat dispersers. Heat dispersion with molds of a given material, iron or brass or aluminum, in still air, at room temperature is a function of the total heat in the mold and the surface area of the mold.
If the mold is going to cast a great big bullet, the mold needs to be big.
If the mold is going to cast a small bullet, the mold needs to be small.
Optimum mold size, for maximum casting speed, is a function of bullet weight, and maybe dimension ratios; but certainly of bullet weight.
Molds are classified as "hot", "ideal" or "cold" here.
"Hot" molds require cooling off between pours, a slow pace of casting that results in fewer good bullets being cast per hour than with an "ideal" mold. An example is my Ohaus 45-405 single cavity (SC) mold that casts 45 caliber 433 grain bullets, but not many good ones per hour.
"Ideal" molds will cast good bullets as fast as you can go through the casting steps, with no waiting time between pour and open-the-mold. These molds are just right; normal, unhurried and un-slowed cycling through the casting steps gives us good bullets, fast.
"Cold" molds require a lot of mold heat-up time and quick casting. If you stop for a bit you get wrinkled bullets. These molds are too cold. An example is my custom #78-185, a 185 grain 30 caliber SC mold that produces wonderful bullets, slowly.
ALLOY EFFECT
Different alloys of lead (Pb), tin (Sn), and/or antimony (Sb) melt at different temperatures. Most of these alloys go through a slushy stage between completely solid and completely liquid. The metals; lead, tin and antimony do not go through a slushy stage. Some alloys have a sharp solid-liquid temperature, with no slushy stage. These are called "Eutectic" alloys.
Here is a table of temperatures where the metals or alloys are solid, slushy (if they are slushy), and liquid. All temperatures in degrees F
Metal or alloy Solid Slushy Liquid Note
38.1% Pb/61.9% Sn 361.4 Not 361.4 Eutectic, "63/37"
Tin 449 Not 449
Linotype 463 Not 463 Eutectic
91% Pb/2% Sn/7% Sb 463 <<Slushy between>> 525
88.8% Pb/11.2% Sb 484.2 Not 484.2 Eutectic
94%Pb/6%Sb 486 <<Slushy between>> 550
90% Pb/ 10% Sb 486 <<Slushy between>> 500
95% Pb/ 5% Sn 522 <<Slushy between>> 597
97.5% Pb/ 2.5% Sn 608 <<Slushy between>> 617
Lead 621 Not 621
Antimony 1166 Not 1166
Source: The Art Of Bullet Casting, Jerry Gonicsburg On "ALLOYS FOR CAST BULLETS"
Note that the numbers given above may vary slightly by source. For example, CAST BULLETS by E.H. Harrison, page 16, has the eutectic lead/antimony alloy as 87.3% Pb/12.7% Sb rather than the 88.8% Pb/11.2% Sb above.
For a continuous although virtually incomprehensible graph of melting points of lead, tin, antimony alloys, see the Lyman CAST BULLET HANDBOOK, third edition, pg. 47.
The important things about this, to me, are that (1) lead, tin, antimony metals and alloys melt at widely varying temperatures, and (2) the melting temperature generally goes down as tin and/or antimony are added to lead.
"Cold" molds may operate OK when casting in linotype or other tin-and/or- antimony-rich alloys such as linotype; this because these alloys melt and solidify at lower temperatures than alloys with higher lead percentage, such as 25:1. An example is the RCBS 22 caliber 55 grain double cavity mold. Some casters report this mold as very cold, others, casting in linotype, report this mold as ideal.
BULLET SHAPE
Pistol bullet molds do not seem as sensitive to the "hot" characteristic as do longer rifle bullets. My guess is that bullet with shapes approaching spherical transmit less heat to the mold than do longer thinner bullets.
AGGRAVATION TOLERANCE
To some degree the "cold"-"ideal"-"hot" characteristic of a mold is a reflection of the aggravation tolerance of the caster. The more blasé casters are happy with molds that drive the more sensitive caster nuts.
MOLD WEIGHT
Many "cold" molds are relatively heavy. I find it easier, less tiring and faster to cast good bullets with a lighter mold; and I am enormously strong. Lighter is better.
MEASURING-THE "IDEAL" MOLD
I took a sample of molds, mine and molds belonging to others, only iron/steel molds. No Hoch molds because the geometry is so different from that of other Lyman or RCBS or NEI or Ohaus molds.
I did a lot of measuring and calculating and casting, and got comments from fellow casters. At the end, there was a pretty clear relationship between the surface area of the mold, (not including the sprue plate), and the nominal weight of the bullet/s. An EXCEL workbook containing all the data, "Mold areas and bullet weight", is in "ERRATA".
Here's how the measurements and calculation were made:
Measure the length, (parallel to the handles), width, (across the mold halves), and height of the mold; then calculate the surface area in square inches.
Divide the nominal bullet weight, (a double cavity 55 grain bullet mold has a nominal bullet weight of 110 grains), by the mold surface area and get "grains per square inch".
The Ohaus 45-405 mold had the largest number of grains of bullet weight per square inch of mold at 49.7 grains per square inch.
The Ohaus mold is "hot" because it has too much lead going into too small a mold.
The custom #78-185 mold had the smallest number of grains of bullet weight per square inch of mold at 15.6 grains per square inch and is too cold because it has too much surface area for the size of the bullet. This mold is "cold" because it has too little lead going into too big a mold.
Molds with between 20 and 40 grains of nominal bullet weight per square inch of mold surface area were "ideal".
FIXES
The perfect fix would be to have mold manufacturers vary mold dimensions to correspond with nominal bullet weight.
When casting with a given mold and alloy we can, and should, adjust the pot temperature to make casting good bullets as fast as possible. A "cold" mold wants the pot and alloy hotter; a "hot" mold wants the pot and alloy cooler. If the alloy is too cool for the mold/alloy combination the bullets will be wrinkled. If the alloy is too hot for the mold/alloy combination the sprue will take a long time to harden, bases will have those rough looking holes at the sprue and the bullets will tend to be frosted.
Allow enough time for the pot temperature to stabilize, experiment with different thermostat settings, and write down the settings and results. A thermometer is handy during this temperature adjustment.
Remember that at some temperature north of 800 degrees F the alloy and/or its constituents begin to oxidize very quickly.
"HOT" MOLD FIXES
(Water + molten lead = explosion. Be very careful with water anywhere near the lead pot.)
From "The Modern American Rifle" A. C. Gould, copyright 1891: "...Before commencing, place a dish of water near you, and a mallet or stick of wood; the first to plunge the mold into when it is growing too hot,"
Now A. C. is talking about a "hot" mold. And what he's doing is cooling the mold off so he can cast faster, so he can get more bullets per hour.
Dick Howes at the Old Colony Sportsman's Association advocated mold cooling by touching the mold bottom or sprue plate to a wet sponge or folded cloth. He was able to cast a lot of good bullets quickly using this method.
Lately, (2008), Bruce B. on the "Cast Boolits" forum has cast amazing quantities of bullets in short times using his adaptation of these cooling methods.
Cast with more than one mold and allow alternate molds to cool between pours.
Cool the mold in a stream of air from a fan.
Cool the mold on an aluminum plate. I've had good luck cooling the bottom of the mold on a flat aluminum plate, and on the bottom of my aluminum muffin pan/ingot mold.
If the mold has two cavities, pouring into just one cavity will reduce the mold temperature and may actually increase production of good bullets.
It has been suggested that replacing the sprue plate on a "hot" mold with a great big sprue plate will make the mold less "hot".
"COLD" MOLD FIXES
Cast a lot with a new "cold" mold. As the mold surfaces oxidize or blue the heat transfer rate seems to go down and the mold gets less "cold". A lot of use doesn't fix the problem, but does lessen it.
Using a mold-prep in or smoking the mold cavity/ies may make the mold less "cold". Some casters suggest using mold-prep on, or smoking, the outside-the bottom and sides of the mold, to make it less "cold" by slowing down heat transfer.
Heat the mold on an electrical hot plate or with a propane torch; or dip the mold in the pot of alloy. These actions may work best when done with varying frequencies, such as before each pour, every second pour, etc.