Hi all,

This is non-bullet related but was wondering if someone here might have an idea.

Short version is a friend of mine recently moved from sea level to 5000 ft above. He has a couple of lead casting machines and has been having an issue with a tiny bubble forming at the sprue. This happens with both his machines.Slowing them down does not solve the bubble issue. I am wondering if this might be caused by some form of cavitation as there really isn't a way for air to get in and if anyone here might have an idea of what to suggest, and if there might be something to add to his mix to try and eliminate the issue?

Thanks,

Mark

Most bullet molds have grooves on the top of the mold allowing the air to escape. Could be the sprue cutter is to tigh against the mold.
Add some tin to the mix.

Jim

I would first try casting at a bit higher temperature. Just as it takes more heat or a longer period of time to boil an egg as your elevation rises, so does it take more heat to do anything else involving heat-to-liquid transfers.

If that doesn't work, he might need to change his alloy slightly. As you doubtless already know, the greater the % of lead in a lead alloy, the more shrinkage there is as the casting cools. Tin (1 or 2%)improves lead alloy flowing in molds, and the addition of antimony reduces shrinkage.

That is why linotype was developed with 84% lead, 4% tin, and 12% antimony as the original standard mix. It enabled typesetters to very rapidly cast almost flawless lines of type for printing machines used until about 1960 to produce newspapers and books all over the world.

(Pure, real, Linotype also has the advantage of requiring MUCH less heat to fully liquefy than does pure lead. And lastly, as a true eutectic, it is totally liquid once it reaches its melt temp, and totally solid when it goes below that stage. No solid then slush, then liquid, or liquid then slush, then solid.