Bullet Mould Materials

Bullet Mould Materials
People have been casting their own bullets for literally hundreds of years.  While the idea of pouring molten lead into a mould hasn’t changed much over that time, the technology used to do it most certainly has.  In this article we’ll be taking a look at the three most commonly used mould materials and discussing the pros and cons of each.

Steel is probably the most commonly used metal when it comes to modern bullet moulds.  Strong, hard, and reliable; it’s also the metal of choice for most large scale mould producers like RCBS, Lyman and Saeco, as well as many smaller custom manufacturers.  The biggest benefits to working with steel are it’s hardness and strength.  Because it’s so much harder than lead, steel moulds can be used to cast tens of thousands of bullets with virtually no wear.  Likewise, a steel mould that’s dropped is far less likely to be damaged, or knocked out of alignment than one made of aluminum, or even brass.  This natural durability, combined with basic maintenance and lubrication enables steel moulds to last virtually forever, making them ideal for high volume casters, or use in automated casting machines.  I’ve purchased and still use quality steel moulds that are more than 50 years old that work just as reliably and accurately as new ones rolling off the line.  That’s not something you can say about many tools these days, let alone those pushing five decades. Another great feature of steel moulds is their ability to retain heat, and do so evenly.  As a result of this property, they tend to yield better quality bullets once they’ve had a chance to heat up, particularly if you’re dealing with large cavities that don’t fill easily.  Steel also has a very high melting point, meaning it’s by far the least susceptible to warping, which can (and does) occur at high temperatures with other materials.

While steel is a great material, it also has some drawbacks. The first thing you’re likely to notice about a steel mould when you pick it up is the weight.  Steel is heavy, which makes it tiring to use for extended periods of time.  Due to this fact, you’ll rarely find any large capacity moulds; the most I’ve ever seen are quad-cavities, and even those are uncommon.  Fewer cavities, of course, means slower production.  Steel also takes longer to heat up than other metals, often requiring 45 minutes or more to get to proper working temperature.  Corrosion/rust is another factor, particularly if you don’t store or maintain your moulds properly.  Unlike aluminum or brass, you can’t just leave these in the shed, particularly in areas with high humidity.  Instead, they need to be cleaned and oiled after every use, including the cavities.  Unfortunately, this means they also need to be degreased before you cast with them again, which can add significantly to prep-time.  Lastly, being a heavier, harder metal, steel is more difficult to machine, which naturally translates to higher production costs and retail pricing.  Though not as pricey as brass, steel will always cost you more than an identical design in aluminum.


If steel is the most popular mould material, aluminum is a close second, and gaining rapidly.  The push by casters for low-cost, high-capacity moulds is prompting an increasing number of  producers to switch to aluminum, or at least offer both choices.  Lee Precision in particular is well-known for their quality aluminum moulds sold at affordable prices.  As aluminum is a relatively soft metal, it’s also very easy (and affordable) to work with.  This in turn helps reduce production costs, which naturally translates to lower retail prices.  Another fantastic quality of aluminum is it’s high strength-to-weight ratio; relative to steel, aluminum is extremely light, making it a pleasure to cast with even when using large capacity moulds.  This unique property allows manufacturers to produce four, six and even larger cavity moulds that simply wouldn’t be practical using steel.  This increased capacity, coupled with the fact that aluminum mould blocks heat up quickly and don’t need to be oiled or cleaned, means casters are able to start churning out good quality bullets just minutes after beginning a session.

As with steel, aluminum isn’t perfect.  The greatest challenge to using aluminum for moulds is likely it’s relative softness.  While aluminum moulds that are treated well and maintained properly can last a long, long time– the reality is they just don’t have the resilience that steel does.  If you drop or open one too forcefully, it’s not difficult to damage them or knock the blocks out of alignment.  If they get too hot, aluminum moulds are also prone to warping, particularly since they tend to heat up unevenly.

Brass moulds arguably represent the ‘happy middle ground’ between steel and aluminum.  Brass is harder, heats more evenly and warps less than aluminum, but is still more resistant to corrosion than steel.  Much like aluminum, brass moulds can often be found with as many as six cavities, making them a great choice for production casting.

When it comes to cons, even brass moulds have their flaws.  For starters very, very few manufacturers use brass due to the high cost of the material.  That in turn results in a similarly high retail price most customers are simply unwilling to pay.  To put that in context, I’ve purchased brass moulds by MP Molds, Night Owl Enterprises and JT Bullet Moulds among others, that cost as much as four times the price of an aluminum mould from Lee Precision would.  Even the most well-heeled would-be caster would likely blanch at the notion of buying half a dozen or more brass moulds all at once.  Likewise, because brass moulds are generally only available from smaller shops, they can be difficult to find with very long wait-lists.  It’s no exaggeration when I say I’ve purchased brass moulds that required me to sign up in advance only to wait more than a year before invoices were issued let alone product shipped. Lastly, as with steel, brass is a fairly heavy metal; although large-capacity moulds are available, they can quickly tire even the most veteran of casters when used for prolonged sessions.


Steel, aluminum and brass moulds are all great choices, and at the end of the day no matter what you select, you’re going to get get quality bullets from any of them.  When making a decision, I always encourage folks to focus less on the cost, and more on what they hope to get out of them.  Factors such as how often you plan to cast, for how many hours, how much time you can devote to maintenance and how long you need your moulds to last are important ones that merit careful consideration.  It’s also important to remember, there’s no rule that says you have to buy every mould you’ve ever wanted all at once.  The collection shown in the video above is one that I’ve built up over a dozen years, which helped to spread the cost out and make it a little easier to bear.

Back in my 20’s I started casting a few days a year for a whole day at a time.  I needed moulds that could withstand that kind of abuse, and last me for many decades to come, so I made a decision to invest in brass whenever I had the option.  It’s a decision I’ve never regretted, and one that’s served me well, to the tune of tens of thousands of bullets at a fraction the cost of retail.  With that said, I also own a large number of steel and aluminum moulds that still regularly make it through my production rotation.

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