I was casting bullets this morning and started having problems that all casters face at one time or another. I got my camera and saved my screw-ups for posterity.
The first problem that we come upon is called flashing. When bullet casters talk about flashing, it's generally because some bit of crud or slag got between the mold halves and the mold didn't close properly. That lets the liquid lead get between the halves of the mold.
When you find flashing, take a minute right there and find the problem. I keep a pair of needle-nose pliers on the bench for problems such as this. In this case, a bit of slag had found its way into the mold pins, and the mold wouldn't close.
The base of the bullet is probably the most important part of the bullet and we want the base of the bullet square and free of blemishes. The picture below shows two rejects.
The bullet on the left shows a concave base, and I can't figure out how that happened. When I knocked the sprue off and dropped the bullet I saw that base and muttered "What the hell?" For some reason, not enough metal got into the mold. This bullet is a reject because of the base.
The bullet on the right shows a problem of not putting enough metal in the sprue. As liquid lead cools, it contracts and if the bullet caster doesn't have enough metal in the sprue, as the metal contracts, it runs out of spare metal and you get a hole in the bottom of your bullet. We call this a void. This bullet is a reject.
Hopefully, your reject pile is small and your bullets come out clean, shiny and useful. I'm liable to use just about anything lead-based as bullet material. Old plumbing pipe, wheelweights, roof flashing, all of it can be recycled into usable bullets.
The objective is a big pile of bullets ready for lubing.
After I lube these bullets they'll be ready to load. All this is recycled material that's been transformed over the course of several hours into something completely useful. Bullet casting is a "green" activity that I've been taking advantage of for many years.