Bullet Casting Part III
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- Last updated: 10/12/2020
Although we invariably refer to ‘lead’ bullets, very few are pure lead, with only black powder shooters using projectiles made of this base metal in its plain form. The majority of ‘lead’ bullets are an alloy, consisting of a mixture of metals, which is significantly stronger than pure lead. The three metals most commonly found in these alloys are lead, tin and antimony. Lead provides weight and density while tin adds some strength. However, its main purpose is to give it ‘fluidity’, so it fills out all of the corners of the mould. Antimony greatly increases the strength of a lead/tin mix.
The ratio in which these metals are combined dictates the strength of the alloy so it is important to source enough of each to be able to produce a metal that is suitable for casting bullets. You need an alloy with the necessary characteristics for casting and shooting; the hardness to withstand being fired and the ability to flow and fill the mould cavities well, to consistently form perfect bullets.
Scrap lead, in the form of old pipe or flashings from roofs, is relatively easy to get hold of from scrap yards, builders or plumbers and it is a good base for your alloy. It tends to require cleaning to remove oxidation, and calcium deposits in the case of old water mains. This can be done manually with a wire brush, or by melting it down.
Old wheel weights used to be a good source of alloy but Europe banned the use of lead for this purpose in 2005. A lot of older, and in particular American literature on bullet casting recommends wheel weights but this is best ignored in the UK.
If you have access to the backstop of a shooting range then this is a fantastic source of suitable alloy. All of the expended bullets are usually already a suitable composition for recasting.
If a lot of .22 rimfire ammo is used, the deposits might be softer and need a bit of toughening up, but otherwise, they are good to go. Some facilities pay to have the backstops cleaned out, so you might be able to do a deal with them and save everyone some money. If you are recovering metal then you should always wear a suitable mask and gloves to avoid inhaling or absorbing toxic substances within the deposits.
Old-style printers, that use cast metal lettering, are an absolute gold mine if you can find one because their scrap is perfect. The metal they use, Linotype, is a hard alloy containing lead, antimony and tin, making it ideal. It can be used to cast higher velocity rifle calibres but is more often softened by mixing with lead and used for handgun calibre bullets. It tends to be very clean and so can be used straight away with no cleaning necessary, plus it can also be used to harden up other alloys you have sourced.
Readymade alloy can be purchased in ingots, premixed to the correct strength for bullet casting, but it is expensive, particularly with postage on top. It is clean and requires no mixing or altering, making it very easy to use, but the cost tends to outweigh any savings that would otherwise be achieved by home-casting.
Once you have your metals sourced then the next step is to mix them to produce bullets of a suitable hardness, which can be rated using its Brinell Hardness Number (BHN). For example, the BHN of Pure lead is 5, Linotype 22, and cast bullets 15 or 16.
The easiest way to check the hardness of your alloy is to match it to a factory-made bullet that works well in your gun. There are high-tech devices available to measure the hardness of metals but when you are first starting to cast these expensive items are not really necessary. Using your alloy, cast a bullet and when it cools test it against the factory one. Scratching the surface or striking it with a hammer and comparing the results are simple methods of testing different metals. Although not precise, they will give you a feel for the comparative hardness of your alloys.
If your bullet feels significantly softer than the factory bullet then you need to add something to harden it, like linotype.
If it feels too hard then adding more pure lead will soften it. Experimenting in this way will help you get an understanding of the different hardnesses that can be achieved and the effects of adding different metals to the alloy.
When you start casting your own bullets, you soon become a ‘scrounger’ and find it impossible to walk past a bit of scrap metal without checking it out. People do still throw away small amounts of lead which are not worth enough to take to the scrapyard, and bullet casting is very much a case of recycling whatever you can source.
There are several sites online that list the BHN numbers for various bullet alloys and a few that allow you to enter your own data and calculate the hardness of your particular mix. The hardness of your alloy is something you can experiment with and, to some extent, customise to your firearm. Being able to develop an alloy that works particularly well in your gun, possibly better than factorymade bullets, is another advantage of casting. There are a few standard factors worth bearing in mind. For every 1% addition of tin the BHN increases by 0.3 and with antimony each 1% increases it by 0.9, but in the case of home casting a trial and error approach is more practical. Once you have made a suitable alloy it is worth casting an ingot and keeping it so you can match your next batch to it.
Next month we will be getting some alloy into the pot and producing bullets, heating, mixing, and fluxing the alloy plus preparing and filling the moulds.