Monday, May 17, 2021

Bullet Casting 103: Casting Bullets

Now that we have a batch of clean alloy formed into ingots, we can move on to actually casting it into bullets.

The same camp stove we used to melt the alloys can be used for rendering ingots. While this keeps costs down, one issue with this method is that it is difficult to maintain a steady temperature in this way. If your melt is too hot, the tin and antimony can separate; if it isn’t hot enough, the alloy will start to harden before it can fill the mold, leading to poor fill-out and useless bullets.

If you go this route, I recommend that you not use the same pot for rendering as you do for casting, as the contaminants we spent so much time and effort filtering out in the rendering process end up caked to the sides of that pot and will end up contaminating the alloy when you go to cast. Instead, either use a dedicated cast iron pot for bullet casting, or use a modern casting furnace. These are electric and have thermostat dials for precise temperature control as well as integral melting pot. There are a number of manufacturers, such as Lee and Lyman, who offer quality products with different features and at a range of price points.

There are two main options when you’re ready to start making bullets: ladle pour and bottom pour casting furnaces. They come in different capacities, but 10 and 20 pound are the most common. 

Two of the author's casting furnaces

Once you have a means to melt your ingots, you need a way to get the molten metal into the bullet mold. With traditional furnaces, or the aforementioned iron pot over a camp stove, a ladle is used. There are a few different styles, and if you’re left handed like me, take note on which side of the ladle the pour spout is located. Obviously, with a bottom pour pot, a ladle isn’t necessary.

Bullet molds are next. One of the nice things about this hobby is that it’s been around for a long time, so used molds are available in plenty.* A new or new-to-you mold will need some prep before you start casting, but usually all that’s necessary is to give the mold a good cleaning with solvent and a nylon or bronze brush. Once it’s clean, put a small amount of heat resistant lubricant on the hinge of the sprue plate and it’s ready to go.

A selection of the author's bullet molds

At the start of a casting session, the mold is at room temperature. Using it now will cause the pour to harden too quickly, resulting in badly formed bullets. To heat the mold, you have several choices:
  • Some casters have a dedicated hot plate they rest the mold blocks on to bring it up to casting temperature;
  • Others will prop the mold on the side of the casting pot; 
  • Some casting setups have a dedicated mold pre-heat shelf.
  • Whatever you do, do not dip the mold in the melt! This can warp the blocks.
Even with preheating, the first few casts are not going to be acceptable. Don’t worry about it, and instead get a good rhythm going so the mold doesn’t cool down.

When filling the mold, make sure to fill the cut out in the sprue plate. This puddle of alloy helps make sure that there’s enough metal to completely fill out the bullet.

Depending on alloy and the size of the bullet being cast, the time for it to set will vary. The appearance of the puddle on the sprue plate can help: when it goes from shiny to dull, wait a few more seconds, then open the sprue plate by hand with heat resistant gloves or knock it open with a wooden stick; separate the handles; and, if all goes well, the bullet should drop out. If it doesn’t, tap the hinge of the mold with the stick. Never hit the mold blocks themselves. If it takes significant effort to get the bullet out of the mold, it likely needs maintenance.

I use a cigar box lined with an old towel to catch my bullets. Don’t drop them on a hard surface as they’re still hot enough to deform!

Shiny, freshly-cast bullets.

Once you’re done with the casting session, it’s common to leave an inch or so of alloy in the bottom of the pot to speed up the melt for next time. Take care if you’re using a bottom pour pot, however, as they can leak. After the mold has cooled, oil the blocks or wrap them in Vapor Corrosion Inhibitor (VCI) paper to help prevent rust.

Please review the safety brief from my previous post and follow proper post-casting hygiene. When everything is done for the day, keep your casting clothes separate from regular laundry and wash your hands and face thoroughly, or (even better) take a shower.

My next installment on this topic will deal with sizing and lubricating cast bullets so they’re ready for loading.

Be safe, have fun, and good casting.

* Editor's Note: David assures me that "available in plenty" is a perfectly cromulent phrase despite the fact that the bad grammar makes my teeth ache.  It may be a regional idiom I've not heard. Either way, please consider this my use of the term [sic]. 

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