by B.B. Pelletier
This report comes at the request of DB, though in the seven months since the last report, many of you have expressed an interest in the subject of casting bullets. In the first report, I showed you how I reclaim the lead from the thousands of pellets shot every year. But that lead isn’t enough for me to cast all the bullets I make. So there are many other sources of lead–many pounds coming from my friend Mac, who is also a bullet caster. I probably have 600-800 lbs. of lead on hand, and perhaps 40-50 pounds of tin. Some of my lead comes from wheels weights, which brings a quantity of antimony with it.
Those are the three elements needed for bullet casting–lead, tin and antimony. For modern guns, the antimony makes the alloy harder so the bullets can be propelled faster. Cast bullets can be fired at velocities up to and sometimes even exceeding 2,000 f.p.s. For black powder guns and airguns, though, hard lead isn’t required or even desired. What they need is a soft bullet that takes the rifling well and obturates (by deforming in a plastic way) when hit from behind with the powerful whack of exploding black powder. That obturation is counted on to seal the bore as the hot gasses push the bullet.
I want you to understand what obturation is in this instance. When a charge of black powder explodes, it’s far more sudden than the rapid burning of smokeless gun powder. The shock wave slams into the base of a lead bullet with greater force than a sledge hammer. Being soft, the lead cannot help but upset, squashing out until it contacts the sides of the bore. This is a characteristic that black powder shooters rely upon when calculating the proper loads for best accuracy. This squashing or filling of the bore is known as “obturation.”
Big bore airguns do not obturate their bullets. The pressure of compressed air is not sufficient to make lead squash and obturate. So, it’s far more important with airguns that the bullet fit tightly in the bore–even to the point of being slightly oversized. Since obturation will not happen, the lead needs to fill the bore at the start of firing. Which brings us to the subject of casting bullets.
You cannot always buy a bore-sized bullet, but if you have the right mold you can always cast one yourself. That’s why the big bore airgunner should look into bullet casting. That and the savings that goes with casting. If the lead can be acquired free or very cheap, the cost of the bullets is virtually nothing. Compare that to spending up to a dollar a bullet, and you’ll quickly see why casting is desirable. Of course, if you’re shooting only 50 big bore rounds a month, then it may not be worth the investment in the equipment to cast your own bullets.
Casting is little more than melting lead and pouring into a mold to harden. It can be done with the most primitive equipment involving nothing more than a campfire, lead and a mold. I use an inexpensive electric furnace from Lee that allows me to control the heat very carefully. This furnace holds up to 20 lbs. of lead, which is more than enough to cast what I want. I load it with a combination of lead and tin, so the result is an alloy of 30-40 parts lead to one part tin. There will be some antimony in the mix as well, but it will be low enough not to matter. I want a very soft bullet.
Pure lead does not cast as well as I need for good bullets. By adding some small amount of tin, I boost the ability of the metal to fill out the mold. The result is a soft bullet that takes the rifling well, obturates well and fills out the bullet mold without voids and areas of missing lead. The result is a clean, sharp bullet of relatively uniform weight. I would expect to pay 40 cents apiece for the bullets I can produce for almost nothing.
I start with a pot full of metal. Starting from a cold pot, it takes 25 minutes for the metal to melt and be ready for casting. When it’s up to temperature, the pot thermostat is turned down to about 650 degrees in stages. The object is to have just enough heat to keep the metal molten. That reduces the fumes, though I always cast outdoors to reduce exposure to fumes.
Things I need
Besides a furnace and lead, I need a plastic hammer to rap the sprue plate, safety glasses for myself, a large towel in which to drop the new bullets so they don’t get damaged, a pair of pliers to pick up lead pieces, beeswax to flux the lead, a cardboard box for the dross and I like a large metal cooky tin cover to catch the sprue as its cut, because I want to put it back in the pot.
Skimming the dross
The pot started with odd bullets and other lead items. When they all melted, there was a portion of non-lead “dirt” floating at the top of the pot–just as there was when I reduced the lead waste to ingots. I use a large steel spoon to skim this dross from the top of the pot and dump it into a cardboard box. Though it’s hot, the box will not burn.
Fluxing the metal
Next, the metal must be fluxed. What that means is the separate metals in the pot must be stirred and combined into a homogeneous mixture or alloy. A piece of pure beeswax the size of a USB plug is used for this. Drop it into the pot and let it melt, then stir the metal, mixing the top and bottom parts thoroughly for a minute. When you’re finished, the lead at the top of the pot should be shiny. During casting, look at it from time to time, looking for a gray scum. That’s tin separating from the lead. When you see it, time to stir the pot or possibly to flux again.
Tomorrow, we’ll be ready to start casting.