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We continue from the first part of our introduction to casting, picking up exactly where we left off last time: finding the optimum material hardness.
Cover photo: determining alloy hardness.
Whether the bullet material is too soft or, conversely, too hard can be gauged to a considerable extent by inspecting the rifling grooves for lead buildup and comparing group sizes, but this is a fairly crude method that requires extra caution. A much more accurate a pproach is to use a dedicated hardness tester. Lee offers one under the name Lead Hardness Testing Kit, priced at CZK 3,154. It is an ingeniously simple device, almost brilliant in its simplicity, and it is also very easy to use. Screw the special die with its spring-loaded indenter into the press and snap the sample holder onto the ram. Take a bullet, file away a little material to create a flat surface, and place it on the holder. Then raise the ram until the indicator aligns with the top of the die. Hold the press handle in this position for 30 seconds, release it, and remove the sample. The indenter will have pressed a dimple into the bullet. Take the miniature microscope with a scale etched into its lens, align it with the dimple, and measure its diameter. The larger the indentation, the lower the material hardness, and vice versa. The hardness can be determined from the diameter, and from the hardness you can in turn estimate the pressures the bullet can withstand. The exact figures can be found in the table supplied with the kit. The pressures your bullet will be subjected to can be estimated using internal-ballistics software, such as the freely available Gordon Reloading Tool. For example, suppose your load configuration generates 16,000 PSI. Find that pressure in the table and you will see that your alloy must have a minimum hardness of 12.5 BHN. However, it is advisable to go one or two hardness points higher, i.e. somewhere between 13–13.4 BHN, which corresponds to an indentation diameter of .062–.063. Did you measure a .070 indentation? Then you will need a harder alloy, a slower-burning powder, or a reduced powder charge. The result will not be a perfect representation of real-world conditions. The equation is simplified and does not account for other factors. If, for example, you have a fast rifling twist rate or high bullet velocity, a slightly harder alloy will be preferable. For our purposes, however, this is entirely sufficient.
The indenter has pressed a dimple into the bullet. Take the miniature microscope with a scale etched into its lens, align it with the indentation, and measure its diameter.
The hardness can be determined from the diameter, and from the hardness you can in turn estimate the pressures the bullet can withstand. The exact figures can be found in the table supplied with the kit.The Lee Precision products mentioned in this article are available from STROBL.CZ s.r.o. More information can be found at strobl.cz, or directly on the manufacturer’s website leeprecision.com
Alloying Alchemy
It should be added to the above that if you intend to use cast bullets for hunting, the softer the lead, the more readily the bullet nose will deform. At higher velocities, it may even have a tendency to fragment. Conversely, a harder alloy provides deeper penetration and better structural integrity. But what can you do if the hardness is not suitable?
Hardness can be increased by adding alloying elements to produce a hard-část alloy. Again, this is a complex subject with a touch of alchemy to it, so I will cover only the basics and refer anyone interested to further study. If you want a harder alloy, antimony and tin are added (although other elements are also occasionally used). A proven ratio is 92% lead, 2% tin, and 6% antimony. Antimony is more complicated to work with because it melts at temperatures at which lead is already giving off clouds of toxic fumes, so it is melted separately and then carefully mixed into the molten lead. Tin, by contrast, melts even more readily than lead, and adding it improves the fluidity and mould fill-out of the alloy. So if your bullets have rounded edges after casting in places where you expect crisp, sharp edges, tin can help. Finding the ideal quantities and ratios is difficult, however, because you are usually working with lead that is far from perfectly pure. One option is to obtain the purest possible lead, or refine it thoroughly, and then add the other elements. A second, less exact but somewhat more practical approach is to work from the hardness of your existing alloy. If it is too soft, add a little antimony, see what effect it has, and repeat the process until you reach the desired hardness. You must not overdo it, however, as an excessively hard alloy can also cause barrel leading. A very rough indicator—and there is not much better available under home workshop conditions—is to clamp the bullet in a vise and bend it to a right angle with pliers. If a network of cracks appears, there is too much of something in the alloy. Soldering tin can be used, and even exotic-sounding antimony can normally be purchased for CZK 2.9 per gram. Alternatively, the alloy can be improved by adding materials that are already harder to begin with, such as the aforementioned wheel weights after they have been melted down. Conversely, if you need a softer alloy, besides selecting the purest possible materials, you can thoroughly remelt the alloy or resort to chemical refining.
Hardening the material by rapid quenching is also worth mentioning. Simply drop the freshly cast bullet into water, which will increase its hardness slightly. However, this only works once the alloy contains a certain amount of antimony. In any case, dropping bullets into water will do no harm even without antimony, and it has the advantage that the bullet has cooled sufficiently before reaching the bottom of the container that the impact will not deform it.
A dedicated hardness-testing kit. Lee offers it under the name Lead Hardness Testing Kit, priced at CZK 3,154.„The casting process itself requires a certain amount of skill and caution—you are, after all, handling molten metal—but fundamentally there is nothing particularly complicated about it!“
The mould cavities must be degreased and smoked before use, which helps the cast bullets release smoothly from the mould.
With the mould closed, pour lead into the sprue holes using a ladle or the furnace’s bottom-pour spout until a puddle begins to form above the openings, indicating that the cavity is full.
Next, knock the sprue plate open, separating the excess lead from the bullets, open the mould, and tap the bullets out.Let’s Start Casting
Load the furnace with ingots and wait for them to melt. Use the lowest temperature at which the molten alloy can still be worked effectively. The fuller the furnace, the fewer problems you will have with temperature fluctuations, and given the time spent on preparation, it also makes sense to cast larger batches of bullets at once. The moulds must be thoroughly degreased, as any grease will adversely affect bullet quality. Conversely, the alignment pins that locate the two mould halves must be lubricated—and only those pins. Beeswax or another lubricant with similar properties is used for this purpose. The next step is to smoke the mould cavities. Simply hold them over a candle flame until a thin layer of soot forms, which helps the cast bullets release from the mould. The mould must then be preheated. If you pour lead into a cold mould, it will solidify before the bullet has had time to fill out completely. You need to establish a consistent rhythm in which the casting process itself keeps the mould at the optimum temperature. The heated top of the furnace is the best place to set the mould down, and the same applies to the ladle. Take care to prevent the molten alloy from coming into contact with moisture, as this can cause an extremely dangerous eruption of molten metal. From time to time, you will also need to skim the oxidized dross from the surface of the melt. If you have a bottom-pour furnace, this can be reduced by adding flux: borax, rosin, or a product specifically intended for bullet casting.
The casting process requires a certain amount of skill and caution, as you are, after all, handling molten metal, but there is nothing particularly complicated about it. With the mould closed, pour lead into the sprue holes using a ladle or the furnace’s bottom-pour spout until a puddle begins to form above the openings, indicating that the cavities are full. Next, knock the sprue plate open, separating the excess lead from the bullets, open the mould, and tap the bullets out. Close the mould and immediately cast the next batch. After filling the cavities, you should wait until the material has solidified. The time required varies depending on the working temperature and bullet size; smaller bullets solidify faster and larger ones more slowly. In my case, with a melt temperature of 370 °C and a .324/177 gr bullet, it takes barely a few seconds—the time needed to set down the ladle and manipulate the mould—so there is practically no downtime. If, after casting, you find an uneven, rounded base or wrinkles on the bullet, this indicates an insufficiently heated mould or a melt temperature that is too low. Wrinkling can also be caused by grease in the mould, while fins or flashing are usually caused by the mould blocks not closing completely. Check whether dirt or other debris is preventing them from closing properly.
Conclusion
Once the bullets have cooled—and, if they were dropped into water, dried—the next essential step is lubrication. The aforementioned Alox works extremely well and lasts a long time, but it must be diluted with alcohol; otherwise, it fouls the dies and produces excessive smoke. I use a 1:1 ratio. Place the bullets in a box, drip a little Alox onto them, and tumble them around until they are evenly coated. Sizing comes next. With Lee dies, this is a simple and straightforward process. Screw the sizing die into the press, snap the sizing punch into the shell holder, place a bullet on it, and operate the press handle to push the bullet through the die and into the collection container. It could hardly be simpler. Randomly inspect the surface quality of the bullets. If it deteriorates, this indicates insufficient lubrication or debris in the sizing die. Clean the die bore when you finish working; with a little care, it will last for tens of thousands of cycles. If you use a gas check, simply place it on the bullet base before sizing, and passing the bullet through the sizing die will crimp it into place. After sizing, lubricate the bullets once again using the same process as before, then leave them to sit for 24 hours, after which you can start reloading.
Sizing is a simple and straightforward process. Screw the sizing die into the press, snap the sizing punch into the shell holder, place a bullet on it, and operate the press handle to push it through the die and into the collection container.More Expensive, but Easier
There is an alternative—or supplement—to alloying that radically reduces the tendency for bullets to strip in the rifling and cause barrel leading, protects the lead from melting under the effect of the hot propellant gases during firing (thereby also reducing the amount of toxic lead vapour in the combustion products after the shot), and helps the bullet seal properly in the rifling grooves: the so-called gas check. This is a metal “protector” that is crimped onto the base of the bullet and, to some extent, performs the function of a jacket. It has its limits and costs extra—one gas check costs around CZK 2.5 depending on caliber—but if you do not want to get deeply involved in alloying, it is a viable solution. When combined with a hard alloy, maximum usable pressures can reach slightly above 50,000 PSI, or around 5,000–40,000 PSI with a less carefully selected alloy. I personally use gas checks with cartridges generating higher pressures. In my case, this is the 8x50mm R Mannlicher, which I load to a pressure of 29,900 PSI. The result is cleaner and more reliable, while allowing me to avoid the pitfalls of alloying. Incidentally, it is interesting that cast bullets can even be given a full metal jacket in a home workshop—for example, cast .223 bullets can be jacketed using cases from .22 LR cartridges. However, these are genuinely advanced operations intended only for experienced, skilled, and dedicated reloaders. Another interesting and considerably simpler process is coating bullets with a special heat-cured powder coating, which serves as a barrier between the toxic lead and the surrounding environment; bullets treated in this way do not require lubrication. But that is a subject for another time.
From left: bullet fitted with a gas check, followed by a bullet without one, and finally an unsized bullet for comparison.Photo sources: Author’s archive
Author: Tomáš Prachař
The article was originally published in Lovec magazine by Extra Publishing
