Ingots with "shrink" holes in center?

I've been smelting my cache into ingots and have another question. I hand sort all the lead as to type/source/whatever. example is battery cable ends, sorted and smelted out about 4lb. ie 2 ingots..... Well some of the ingots, mini, medium and regular muffin pans, have what I call "shrink" holes in the center. It is where the pour shrinks and leaves a "crystal" lined hole in the center of the ingot. This is not in all of the lead but some of the alloys have it in almost every ingot I poured. What is this telling me? The soft types seem not to have this. Any explanation? Thanks, 10

Alloys with more antimony will tend to do this more than pure lead. The alloy shrinks some as it cools. Not a problem at all.
Think of it as a good way to help keep them separate.

Close anyway.
Pure lead just gets a depression in it.
Lead with a little antimony gets the shrink hole like you described.
Lead with a lot of antimony does not shrink at all.
I never really paid attention to the effects is tin in this case.

My observations match LWKnights. Also, the higher the pour temp, the greater the shrinkage cavity on the ingots. Good luck.