This was a great article I stumbled on while reading about bullet molds. I take no credit for this article in anyway and have not altered it; and give Dave France props for a good read. Enjoy.
SUGGESTIONS FOR CASTING BULLETS
by Dave France, 6th Wisconsin Infantry
1. INTRODUCTION. Magazine articles and the instructions that accompany electric melting pots and bullet molds provide basic information about casting lead alloy bullets. However, the information is written about casting small bullets and is inadequate (or incorrect) for the needs of many black powder shooters. Many black powder shooters cast bullets in the 400 to 500 grain weight range that are more difficult to cast than light weight bullets. Minie bullets are particularly difficult to cast well. The objectives of this article are to help black powder shooters to: 1) cast good quality bullets (particularly Minies), 2) understand the alloys used for breech-loading and cartridge firearm bullets, and 3) minimize the time spent casting bullets.
I have found three published sources helpful for casting information. All focus on casting smaller caliber bullets from lead alloyed with tin and antimony. Those sources are:
Cast Bullets and the Cast Bullet Supplement No.1, published by the NRA
Lyman Cast Bullet Handbook, published by Lyman Publications
Jacketed Performance With Cast Bullets by Veral Smith
If you only cast soft lead, you probably don’t need any of the references listed above. I found Veral Smith’s book the most helpful. However, the book is no longer available. If you are going to cast with alloyed lead, I recommend Cast Bulletsby the NRA.
Most of the information and suggestions in this article are contained in one or more of the sources listed above. Several N-SSA members also contributed significantly to this article after reading earlier drafts.
There is considerable variation in the techniques used for casting bullets, particularly for Minies. Because of the variations in techniques that are possible and the many variables that affect casting bullets, it isn’t possible to describe one technique that will prove successful for every bullet and mold. You should develop a technique for each bullet you cast.
2. CASTING PROBLEMS.Incomplete filling of the bullet in the mold and cavities are the most common problems we find in casting bullets. Incomplete filling may result in minor defects (wrinkles or rounded corners on the bullet where the corners in the mold are sharp) or more serious, obvious defects. Incomplete filling may occur if: 1) The melt temperature is too low as it is poured or the melt cools rapidly before the cavity is completely filled. 2) The mold is not held against the spout of the dipper or pot long enough. 3) Air does not vent from the mold well slowing flow into the mold. 4) Air is trapped in the mold.
Cavities in cast bullets may be caused by shrinkage of the melt as it cools or by trapped air. Shrinkage cavities are small and are mentioned in most references about casting bullets. However, cavities resulting from trapped air can be very large. They are not mentioned in any reference I have seen, and as far as I know, occur only in Minies.
A shrinkage cavity forms in the last part of the melt to solidify. The melt usually cools and solidifies in the mold from the bottom of the cavity upward. Consequently, shrinkage cavities generally occur near the top of the mold (in the nose of the bullet if it is a nose pour mold). If the last part of the melt to solidify is in the sprue (the extra metal we leave on top of the sprue cutter), there will be no shrinkage cavity in the bullet. Sometimes if we cut off the sprue too quickly, we can see a cavity appear at the tip of the bullet. Pure lead shrinks about one percent as it cools; harder lead alloys shrink even less. Consequently, shrinkage cavities are small.
Many black powder shooters have more problems casting Minies than round balls or conical bullets (solid bullets). The large surface area of the mold and core plug contacted by the melt as it flows into the mold is the major cause of these problems. The large surface area cools the lead faster than would occur with a mold for a similar weight conical bullet. Some bullet casters find large cavities from trapped air in the base of Minies. They are more common when using a bottom pour pot than when using a dipper. However, some Minie casters are successful at casting Minies with a bottom pour. With the bottom pour pot, if the melt is allowed to pour vertically into the mold (along the axis of the bullet), the rapid solidification of the skirt and the outer skin of the bullet may trap air in the mold cavity. The use of a dipper eliminates trapped air by changing the direction the melt is introduced into the mold.
Some bullets may be difficult to cast because of the design. A small meplate (bullet nose diameter) can be a disadvantage for a Minie since it slows the flow of the melt into the mold. Some molds are made with the hole in the sprue cutter and the meplate out of line, reducing the flow even more than a small meplate by itself. A thin skirt (particularly with a very heavy Minie) is another design feature that can make casting Minies more difficult. In general, heavier Minies are more difficult to cast than lighter ones.
3. BULLET MOLDS.The bullet caster should be aware of several considerations in selecting a bullet mold. If problems occur with casting good bullets from a mold, some changes to the mold may be helpful.
Mold materials. Most molds are either a good quality cast iron (usually nodular iron) or a good quality, heat-treated aluminum. There are advantages and disadvantages to both materials. Cast iron molds are heavier and may be tiring to use. On the other hand, cast iron is more wear resistant and less vulnerable to damage than aluminum. Furthermore, cast iron stands up to high temperature well and is more resistant to warping than aluminum.
The faster cooling of the melt that occurs in aluminum molds can cause bullet casting problems. The melt cools faster in an aluminum mold than in a cast iron mold because of the much higher thermal conductivity of aluminum. The thermal conductivity of brass is also much higher than iron and only slightly lower than aluminum. To avoid problems associated with faster cooling in an aluminum mold (particularly with a heavy bullet), the melt may have to be hotter than required for a cast iron mold. (Jacketed Performance by Veral Smith, pg. 63).
The sprue cutter. Some molds have a flexible thin steel or aluminum sprue cutter. A flexible cutter can deform from the load of the cutter attachment screw and cause a leak between the cutter and top of the mold blocks; a more rigid cutter helps to prevent this leakage. (Overtightening the screw will tip the sprue cutter slightly and increase the leakage.) All of the custom molds I have seen have a thick steel sprue cutter. The cutter should be 3/16 (0.188) inches or more thick, and it should be ground or machined to a very flat surface on the mold side to help prevent leakage. Additional advantages of the thicker sprue cutter are: 1) It provides improved sealing while pouring because of a larger contact area between the cutter and spout of the dipper or pot. 2) It also helps form a thicker sprue that aids in preventing cavities in the bullet.
The mold manufacturers seem to use one size opening in their sprue cutters: about 1/8 (0.125) inches. An opening of 1/8 inch works well for a small bullet or round ball but may not for a large bullet. Enlarge the opening to introduce the melt into the mold faster and help eliminate casting problems. I use a 3/16 inch opening for large bullets. Be careful not to make the hole larger than, or out of line with, the meplate diameter. The enlarged hole should be a chamfered hole (or conically shaped hole) through the entire thickness of the cutter. Chamfering the enlarged hole is necessary to provide a sharp edge to cut off the lead sprue. Be careful not to leave a burr on the bottom size of the cutter that will damage the top of the mold blocks.
There are two things that are helpful in preventing the sprue cutter from binding: 1) Add a small amount of lubricant between the bolt head and sprue cutter and between the sprue cutter and mold. Some use a small amount of bullet lube; others use a high temperature lubricant. The makers of aluminum molds generally recommend a lubricant to prevent galling of the mold. 2) If your mold does not have a spring washer, remove the washer that is under the bolt head and replace it with one. The spring washer may be a Belleville washer (a washer with a slight conical shape) or a lock washer (a split washer). Either type of washer will help to prevent the sprue plate from binding as the mold expands.
Guide pins. Large diameter guide pins are less prone to damaging the mating face of mold block than small pins. The damage can raise a spot on the mold face that causes a leak resulting in a fin on the bullet. If guide pins project too far, they will damage the mating mold block. If the guide pins do not project far enough, they will not align the two halves of the mold cavity and will produce an out-of-balance bullet. Always close the mold gently to avoid damage from the pins.
Core plug. As noted in Section 1, a thicker skirt (at least 0.060 inches) can aid in casting good Minies. This is particularly important for casting Minies that weigh 450 grains or more. If necessary, increase the skirt thickness by machining of the plug or by making a new plug. I have found that a very thin skirt is not necessary for a Minie to achieve good accuracy, even with light loads, if the lead is very soft.
Captive core plug. We can increase our casting rate for Minies if the mold has a captive plug. Some Minie casters have a machinist modify their Minie molds to convert to a captive plug. The increased casting rate (which is an advantage in itself) helps keep the mold hot enough to produce good quality bullets.
Retaining plate for the captive core plug. Like the sprue cutter, the retaining plate should be flat steel that is unlikely to be bent out-of-flat. A plate thickness of 0.100 inches works well on the Minie molds I have.
4. CASTING EQUIPMENT. Some suggestions for equipment that will help cast good quality bullets follow:
A large capacity electric melting pot (or furnace). I strongly recommend using a large capacity (20 pounds or greater) electric melting pot. I used a pot over an open flame for a few years. Changing to an electric pot made casting more pleasant and resulted in casting bullets at a faster rate. A large capacity electric pot is an advantage over a smaller capacity electric pot. The larger pot helps to maintain a consistent melt temperature and will provide a more consistent flowrate rate than a small pot.
All electric pots come with a thermostatic control that senses the lead temperature. Some come with a control that can be set to a temperature. Others come only with a number control (a disadvantage in my opinion). You will need a thermometer if you use the latter type of pot. The thermostatic controls are not always adjusted correctly on new electric pots. If you buy one, make sure it will bring the melt to at least an 850-degree peak temperature.
There are two basic types of electric melting posts: 1) bottom pour pots and 2) the pots made for use with a dipper.
Bottom pour pots. We can cast bullets at a faster rate (more bullets per hour) with a bottom pour pot than with a dipper. The bottom pour pot also permits casting while sitting. Over time, a leak or a slowing of the melt flow will occur with bottom pour pots because of dirt collecting in the valve. Occasional cleaning of the valve resolves the problem. I have owned an RCBS electric pot for fifteen years that has served me very well. In my opinion, bottom pour pots are best for bullet casting needs except for some Minies. However, some black powder shooters report good success casting Minies with a bottom pour pot.
Dipper pots (or furnaces). Many bullet casters use dipper pots for all their casting. Many prefer them only for casting Minies. If you decide to use a dipper, you will find a dipper pot is much easier to use than a bottom pour pot (with the dipper) because of the larger opening of the pot and the unencumbered entry into the pot. The larger opening is also convenient for melting scrap lead or large ingots.
Some authorities state that lead can be poured into a mold faster with a dipper than with a bottom pour pot. That may be true for some bottom pour pots, particularly for the small pots. However, my RCBS pot will fill a one pound ingot mold in about three seconds at the highest flow adjustment. I have never had to enlarge the spout opening or even use the highest flow setting. Enlarging the opening may be helpful for some types of pots, but will require a new metering rod made to fit in the larger opening.
Ladles and dippers. A dipper with a spout (with a hole in it, not an open ladle) can introduce melt into the mold faster than a ladle if the dipper spout is held directly against the mold opening. The dipper should have enough metal around the spout to permit drilling the hole to a larger size. (The RCBS dipper is excellent). Drill out the hole in the dipper to increase flow of the melt through the mold. A hole size of about 3/16 (0.188) inches works well for me. It may be helpful to further increase the hole size, but be careful not to make the hole too large to work well with the opening in the sprue cutter. Making the hole larger than the hole in the sprue cutter will not help to increase the flow into the mold.
A large capacity ladle (without a spout) is handy for melting small amounts of lead and for dipping alloy from the pot to cast one pound ingots for later use. A ladle of about 1 1/2 to 2 pounds capacity works well.
Hardness testers. A hardness tester takes the guesswork out of using lead from different sources. I have tried two inexpensive hardness testers. The Saeco tester works very well but has the disadvantage of not providing a direct Brinell reading. I have had an LBT tester for several years and I use it more than I expected. It provides a hardness reading in the Brinell scale and is easy to use. Unfortunately, the LBT tester is no longer available.
The NRA publication, Cast Bullets, pg. 102, states the traditional thumbnail test is not an accurate means of judging the softness of lead for Minies. The hardness tester offers the bullet caster a more accurate means to judge the suitability of lead for casting Minies. Similarly, if you cast harder bullets for a breech-loading firearm, the tester will provide the means to ensure the hardness is what you need. If lead alloy bullets produced at different times have the same hardness, they should perform the same.
5. LEAD ALLOYS. Lead alloy hardness is measured in the Brinell hardness scale. Pure lead has a Brinell hardness of about five. Hardness relates to strength. Consequently, harder bullets are stronger and more resistant to deformation and barrel leading than a pure lead bullet. The more common types of alloy used by black powder shooters are the following:
Soft lead. Some refer to soft lead as pure lead, but it is not 100 percent lead. Soft lead is frequently about 98 percent lead with small amounts of other materials. If the other materials do not raise the hardness too high, the lead can still be used for Minies. The hardness of the Minies I have used over the years has varied from five to eight (measured with my hardness tester). The bullets with an eight hardness shot very well. However, they were very heavy, and I used a very heavy powder charge, which helped them to expand and shoot accurately. A light bullet and/or powder charge might not work well, and I know other black powder shooters have had problems with Minies at an eight hardness. I can’t say with certainty what the maximum hardness lead is that will work for any Minie design, but it is probably six or seven.
Lead-tin alloys. The addition of tin to lead increases the fluidity of the alloy and increases the hardness of the alloy. Improved fluidity helps to cast bullets that are completely filled out. As center fire cartridges were developed in the nineteenth century, higher pressures and velocities necessitated the use of harder bullet alloys. Lead-tin alloys (without other alloying metals) answered the need for harder alloys at that time.
Many black powder shooters buy tin to add to soft lead. Reloaders of modern ammunition do not commonly use alloys of lead and tin (without antimony) for casting bullets. They find it cheaper and more convenient to buy alloys with tin and antimony (since they are part of the alloy as purchased) rather than to add large amounts of tin to pure lead.
Tin begins to come out of the lead-tin mixture at about 725 degrees and forms most of the dross on the top of the melt. Consequently, alloys with tin are usually cast at 750 degrees or less to preserve the tin in the alloy. The loss of tin is very slight at 750 degrees or below and has very little effect on bullets cast by black powder shooters.
The addition of four percent tin to pure lead (at an initial Brinell hardness of five) will increase the hardness to about ten. However, if soft lead has traces of antimony in it, the hardness will increase to a higher level. If tin over three percent to four percent is added to pure lead (without antimony), the hardness increase will not be proportional to the amount of tin added. See the hardness chart which follows. Note an increase in tin from four to ten percent only slightly increases the hardness.
Many black powder shooters add small amounts of tin to soft lead to aid in casting good quality Minies. Of course, Minies need to be soft to perform well in muzzle loading firearms, but one to two percent tin may not cause Minies to be too hard to shoot well. However, we need to be cautious in adding tin for casting Minies. The soft lead we buy may have small amounts of tin and antimony. The addition of one percent tin to soft lead may make it too hard for Minies. Users of tin for Minies also need to be aware that the bullet hardness will change with time. Pure lead with tin will become softer with time, but lead alloyed with tin and antimony will become harder. (Jacketed Performance by Veral Smith, pg. 56 and Cast Bullets by NRA, page 102). Minies cast from soft lead with added tin may initially be soft enough to use, but the increase in hardness that occurs within a few days may make them too hard.
If we use a good quality Minie mold (designed well for casting), good equipment, and good casting methods, adding tin isn’t necessary.
Lead-tin-antimony alloys. The lead-tin-antimony alloys (harder than lead combined solely with tin) help prevent leading and permanent deformation of the bullet in the barrel; both problems cause loss of accuracy. Some black powder breech-loading firearms require harder alloy bullets to achieve the best accuracy. The accuracy of breech-loading firearms with pits in the bore or a rough bore can sometimes be improved by increasing the bullet hardness. Bullets cast from harder alloys have worked well in all the breech-loading firearms I have owned. These alloys are a bargain for many bullet casting needs if they can be purchased for less than or the same price as soft lead.
Antimony added to lead increases the hardness more than tin. (Cast Bullets by NRA, page 103). Generally antimony and tin are both included in hard lead we buy. Very small amounts or arsenic will probably also be in the alloy to increase hardness; the arsenic magnifies the hardening effect of tin and antimony. Most reloaders of modern ammunition do not change the alloys they buy except by adding tin to improve fluidity.
Lead we buy containing arsenic and antimony (both are toxic) cannot be heated (with the equipment we use for casting) to a temperature that will cause toxic vapors. Similarly, removing tin and antimony is not feasible. If these alloys are held at 850 to 900 degrees (the limit for most electric pots), a very small amount of tin can be skimmed off, but all the antimony will stay in the alloy. Adding antimony to a lead–tin alloy is difficult and not common practice reloaders.
These alloys can be heat-treated to increase hardness or can be dropped into water from the mold to increase hardness. See Jacketed Performance by Veral Smith or Cast Bullets by the NRA for more information. However, the properties (after aging) of the alloys listed below are probably adequate for black powder firearms without heat-treating.
A chart showing the approximate hardness of the more common alloys used for casting bullets follows:
Alloy Brinell Hardness
Soft Lead 5 to 8
Lead-Tin (2% tin) 8
Lead-Tin (4% tin) 10
Lead-Tin (10% tin) 11
Wheel Weights 11 to 12
Wheel Weights plus 2% tin 13 to 14
Number 2 Alloy 15-16
Wheel weights. The softest (and least expensive) lead-tin-antimony alloy is wheel weights. Wheel weights are reasonably consistent and are the favorite alloy of many modern reloaders. They produce an alloy that casts well. Some bullet casters add tin to improve the fluidity of the melt and increase the hardness. I have cast bullets from wheel weights with one percent added tin, and I have added soft lead to reduce the hardness of bullets. The added tin did not improve the quality of the bullets. Adding soft lead greatly reduced the quality; many of the bullets did not fill out completely. I use straight wheel weights to cast the bullets for my percussion Sharps carbine and rifle, for 45 Colt bullets, and for bullets for a cap and ball revolver.
Wheel weights can be purchased at a very low price from tire stores, or they may give them away. Unfortunately, they come mixed with dirt and other junk. If you cast bullets with wheel weights, melt the wheel weights outside the home, unless you don’t mind moving out of your house for a day or two afterwards. Remove all of the dirt and debris from the melting pot that you can and cast the metal into ingots for later use. Use a fluxing preparation as you melt the weights to reduce the need to flux while you are casting bullets. (See Section 7). When you melt the ingots later for casting bullets, they will produce almost no smell.
No. 2 alloy. Many casters of bullets for modern and black powder firearms use No. 2 alloy. It was originally a mixture of 90 percent lead plus five percent tin and five percent antimony. Today, an equivalent alloy (producing the same hardness bullet) will have more antimony than tin. For several years, I purchased (at considerable expense) No. 2 alloy from a reloading shop and used it for the bullets for my breech-loading firearms. Eventually, I found No. 2 alloy had no advantage (other than convenience) over wheel weights. (Too soon old; too late smart.)
Linotype alloy. The hardest of the alloys described here is linotype alloy. For many years, linotype alloy was purchased by reloaders in the form of scrap linotype and made excellent bullets for modern cartridges. The linotype alloy had enough tin to help cast bullets that otherwise would not cast well (very long bullets). But linotype is about as common as a 1950 Ford today. Nevertheless, some bullet casters still buy linotype lead or an equivalent alloy. It probably is harder than required in black powder firearms, but some black powder shooters use it with good success.
6. PREPARATION. Careful preparation before casting reduces the time to obtain good bullets and may help eliminate some casting problems.
Prepare one pound ingots of lead (or alloy) before casting. Adding large pieces of lead while casting greatly lowers the temperature of the melt and will add dirt. The lower melt temperature may cause the problems discussed in Section 2. If you buy lead in large pieces, it is best to set aside time to cast enough one pound ingots to last for several casting sessions and to flux to clean the lead of any dirt and debris. (See Section 7).
Clean the mold. Cleaning grease and oil from the mold with a solvent saves time in casting bullets without defects. Denatured alcohol works well; rubbing alcohol leaves some slight chemical residue. Even more important, cleaning the cavity, the vent lines, and the matching faces of the mold block of collected dirt and small bits of lead can prevent casting problems. I use a small brass brush (made for the Dremel tool) or a firearm cleaning brush turned in a drill press to cleancast iron molds (not aluminum). If there are any small bits of lead in the mold, they can be removed by heating them with a small flame from a propane torch (to soften it) and wiped away with a small wood carving tool (such an X-Acto hobby knife) or a thick piece of cloth. If the vent lines are plugged they should be cleaned with the same knife or the tip of a very small file. Be very careful not to nick or scratch the blocks.
Preheat the mold before casting. Don’t waste your time casting bullets to heat the mold to a temperature adequate for casting good quality bullets. First, if the pot has a ledge to hold the mold, start heating the mold by placing the mold on the pot while the lead is melting. Second, if the pot design permits, place the mold so the end of the sprue cutter is in the melt as it heats up; this should bring the mold close to the temperature required for good casting.
Finally, if you are using a cast iron mold, carefully heat the mold with the small flame of a propane torch. Run the small flame over all the outside surfaces of the mold. Do not let the flame touch any of the inside surfaces or enter the mold; it will leave deposits if you do. You will probably be able to skip this last step if you leave the tip of the sprue cutter in the lead long enough and/or if you smoke the mold. Heating an aluminum mold with a torch may damage the mold. It may seem risky to heat a cast iron mold with a torch; some manufacturers recommend against it. However, may bullet casters (including me) preheat their molds with a torch without a problem.
Smoke the mold cavity. We can use the smoke from a match, a cigarette lighter, or a carbide lamp to coat the cavity of the mold to help cast good quality bullets. The thin layer of carbon left by smoking acts as an insulator and slows cooling of the melt in the mold. The delayed cooling helps to eliminate some casting problems. “Mold Prep” (a liquid) sold by Rapine works similarly. I usually use a carbide lamp to smoke the mold cavity before starting to cast, and it is surprising how much it improves the quality of the bullets cast from some molds.
7. THE BULLET CASTING PROCESS.
Fluxing (and Cleaning). Fluxing refers to cleaning the melt to remove dirt and small particles of oxides. Fluxing also refers to remixing tin contained in the dross back into the melt. Fluxing consists of: 1) Scraping the bottom and sides of the pot to release any dirt into the melt. 2) Adding a fluxing preparation to the top of the melt and thoroughly stirring the preparation through the melt and dross at the top of the melt. The fluxing preparation may be a commercial product, beeswax, or bullet lubricant. 3) Skimming the dross and dirt from the top of the melt. Most authorities recommend frequent fluxing. Some authorities suggest fluxing every fifteen minutes and every time alloy is added to the melt to keep the tin mixed well with the lead. Frequent fluxing may cause a problem in casting large bullets (particularly Minies) that would not occur in casting smaller bullets. The time spend fluxing will cause a drop in the mold temperature that may result in poor filling of the mold and a reduction in bullet weight. On the other hand, frequent fluxing helps to keep the melt clean of the small particles of dirt and oxides that will cause bullet quality problems. Some of those problems are: 1) A reduction in bullet weight. (Dirt is lighter than lead). 2) A duller bullet surface caused by the oxide freezing out on the bullet surface as it cools. 3) Cavities in the bullet.
If the small ingots we add to replenish the melt were fluxed well while they were prepared, we can flux less frequently. (See Section 6).
The frequency of fluxing is an individual decision. Many bullet casters (including me) only flux the metal as they prepare ingots before casting, at the beginning of a casting session, and after a long break. Others flux if they see a change in the appearance of the bullets or begin to see cavities.
With the casting of harder alloys, very little tin and no antimony is lost if the alloy is not fluxed while casting. Use of a bottom pour pot helps reduce the loss of tin since only a small amount of tin will enter the dross if it is undisturbed by a dipper and if the melt is kept at 750 degrees or less.
With the casting of soft lead, we need not flux to mix tin back into the melt. We are not trying to mix alloying elements with the lead. If we do not use a fluxing preparation when removing the dross, most of the dross removed from soft lead will be lead. The dross can be melted after several pounds have been collected and most of the lead will be recovered. After remelting the dross, only a small amount of gray powder will remain that should be discarded.
Begin casting at a high temperature. 850 degrees for soft lead and 750 degrees for alloys with tin work well for me. Starting at a high temperature helps reduce the time to cast good quality bullets.
For bottom pour pots. 1) Hold the mold opening against the spout. 2) Open the valve and hold the mold against the spout for a couple seconds after it is filled. 3) Separate the mold and the spout. 4) Pour additional melt on top of the sprue cutter if the sprue remaining after step 2 is not large enough to keep shrink cavities from forming in the bullet. If you need to pour additional melt, you may find it faster to close the valve as you separate the mold and spout rather than adding another step.
Note that the valve may have to be adjusted to slow the flowrate if the flow is greater than required. The adjustment limits how far the operating rod can be raised. I adjust the flowrate down from the maximum for all the bullets I cast, including Minies, but my RCBS pot has a very fast flowrate if opened fully. I use a much lower flowrate for small bullets and round balls than for larger bullets. After finding the correct flowrate adjustment, always open the operating rod to the stop. I have found it necessary to keep the spout in contact with the mold until after it is filled to cast bullets with a sharp edge at the base. Molds and the bottom of the spout were designed to fit together without leaking.
Some bullet casters use a different method with bottom pour pots with good success. Tony Bagdon, the designer of the Hogdon Minie, reports he casts Minies without cavities with a bottom pour pot. Tony also has had success casting other Minies (most heavier than the Hogdon Minie) with a bottom pour pot. He adjusts the flowrate down from the maximum opening, and uses a relatively high 850 degree melt temperature . Tony rests the mold on a mold guide as he pours to allow him to leave a consistent small gap between the spout of the pot and the mold. He tilts the mold slightly as the melt enters to prevent trapping air and creating a cavity. In an old publication by Major George Nonte, he stated that he preferred casting with a gap also.
For using a dipper. Fill the dipper until almost full. Hold the mold (with the opening horizontal) against the dipper. Turn the dipper and mold together while maintaining contact. Hold the dipper against the mold for a couple seconds after the mold is filled. Pour a generous sprue on top of the sprue cutter if necessary to prevent cavities.
The sprue should be the last part of the melt to cool. Be careful not to open the sprue cutter before the sprue is completely cooled. Early opening of the sprue may smear lead between the blocks and the cutter. It may also cause a cavity in the bullet. If cooling of the sprue takes too long, try touching one edge of the sprue cutter to a wet sponge in a shallow container of water. Moisture on the sprue cutter will evaporate quickly, but be very careful not to allow moisture to be carried into the pot. (This is one of the suggestions from the NRA Cast Bullets publication.)
After casting for a time, problems may occur when the mold temperature becomes too hot. The typical problems are frosty appearing bullets and whiskers (caused by some of the melt entering the vent lines of the mold). After casting a quantity of bullets, it generally is necessary to lower the temperature of the melt. Experiment to determine the best casting temperature and strive to consistently keep the mold and melt at the best temperature.
Keep the mold and melt temperature from dropping while casting. You can keep them hot by following the suggestions that follow:
1) Cast at a good rate.
2) Limit delays or breaks while casting.
3) Fill the mold and leave the mold where heat from the pot will help keep it hot if a delay is necessary. If possible leave the mold with the tip of the sprue cutter in the melt.
4) Add lead or alloy in one pound ingots after about one pound of the melt has been removed (unless you use two pots – see item 6 below). If larger amounts of lead are added, the melt temperature may drop enough to cause casting problems.
5) If a bottom pour pot is used, make a steel wire basket that fits into the top of the pot unless you use two pots. Using the basket will prevent cooling the melt that enters the mold from the bottom of the pot and helps prevent the melt from solidifying in the valve. Always keep the level of the melt above the bottom of the basket while casting. Add to the melt by placing ingots in the basket instead of dropping them into the bottom of the pot.
6) The best way to keep the melt temperature high and consistent is to use two pots. Using two pots avoids dropping the melt temperature every time an ingot is added and frequent adding of ingots is unnecessary. Use one pot to cast from; use the other pot to melt the ingots and to provide hot melt for the casting pot. If you want to cast lead at 850 degrees, and if you use two pots capable of keeping the melt at 850 degrees, you should have no problem keeping the melt in the casting pot at the desired temperature. Or for casting at a lower temperature, the melt in the casting pot can be kept at a near constant temperature. I use two pots for all my casting. I find it helpful in casting good quality Minies. I use two pots for casting round balls and conical bullets also because of the convenience.
Frosty-looking bullets. If the mold and melt temperatures are very high, frosty-looking bullets may result. The frosty look is due to a metallurgical change to the alloy at the outer surface of the bullet. If the thin outer skin is scraped away, the bullet looks normal. Some authorities state they should be remelted. Other authorities state they are more consistent in weight than normal appearing bullets. Cast Bullets, page 137, states that evenly frosted bullets are not harmed by the frosting except for a slight reduction in diameter. I shoot them, but sort them into my second class of bullets along with others that have minor defects. As far as I know, they do not cause an accuracy problem.
8. LEAD POISONING. The NRA publication, Cast Bullets, page 42, has a thorough discussion of this potential problem. To summarize very briefly: 1) Lead poisoning caused by casting bullets is very uncommon. Very long exposure to fine dust is necessary to cause a problem. 2) Use adequate ventilation (a fan, not necessarily blowing through a door or window open to the outside). 3) Keep the temperature of the alloy down to limit vapors. 4) After casting or handling lead, wash before smoking or eating.
9. SOME FINAL COMMENTS.You probably will be able to cast good quality bullets without following all the suggestions in this article. There is some art involved in casting and it takes some experimentation to find what will work best.
Don’t leave casting to the last minute, and leave adequate time for casting. You will probably cast three times as many good bullets in two hours as you will in one hour if you consider preparation time. I usually watch video tapes while casting and I don’t mind casting for three or four hours at a stretch with only short breaks.
It is worth the time and expense to buy good equipment if you want to cast good quality bullets. If you have a mold that gives you problems, buy one you know works well for others. I have owned molds that would not consistently produce good Minies and others that made casting easy.