Casting bullets

I got an email from a guy who reads over at my other site, and I thought that it is important enough to include in full here.

Jerry Howell asks:

What causes wrinkles or lines on cast bullets?

Whoohee! Jerry asks a very simple question with a complicated answer. One that has plagued bullet casters for years.

Generally, the wrinkles or lines on cast bullets are caused by a cold mold. As liquid metal flows into the mold it starts to cool. If the mold isn't hot, or if the mold has a cool spot the metal cools at a different rate in that spot. We call these rejects and they go back in the pot. I generally experience ten to twelve rejects before the mold is hot enough to cast good bullets. You will know that the mold is hot enough when the puddle of melt on the sprue stays liquid for three seconds.

As the lead cools in the mold, the metal shrinks just a bit. You want the puddle of metal on the sprue to be big enough to continue to fill the bullet. If that puddle of metal isn't big enough, the bullet cools without enough lead to fill the mold and you get a void in the bullet. Sometimes the void is simply a hollow place in the bullet. Other times the void will be visible and will look like a wrinkle or an incomplete area near the base of the bullet.

Sometimes wrinkles are caused by using really pure lead. Truly pure lead tends to not want to flow and you will see wrinkles. Add a little (2% to 10%) tin to the alloy to increase the flowability of the melt. Insufficient tin sometimes shows up as wrinkles, sometimes shows up as places near the lube grooves that aren't fully filled. You can get tin at any hardware store in the form of "lead free" solder. It comes in rolls. You can also find tin at a salvage yard. Wheelweights have tin in the alloy. Putting a pound of wheelweights in the melt with twenty pounds of pure lead increases the flowability to the point that the bullets fill out completely.

Not prepping your mold can cause wrinkles. With new Lee molds, it is important to smoke the cavity with a butane lighter. I play the flame across the open cavities for just a few seconds before casting with a cold mold. This burns out any oil or grease that might be present and deposits a very thin layer of soot that tends to help me get casting more quickly.

If you are casting with a dipper and pouring the lead into the mold, the dipper must be hot. Stir it in the lead for a few seconds, until the lead doesn't stick to it. If lead doesn't flow smoothly through it, the bullet won't fill completely. This can cause voids and wrinkles. On a bottom flow pot, sometimes the flow hole becomes clogged with trash and the lead can't flow smoothly. This will cause problems, too.

Wrinkles on bullets are a simple question with a complicated answer. Generally, the mold isn't hot enough to cast and simply dumping those bullets and recasting will get the mold hot and good bullets will start falling after six or eight tries. Establish a good steady rhythm and soon the bullets will start to flow. But, be aware that wrinkles can be caused by those other factors I mentioned, too.

I hope this helps.