Right Miller. This same initial shrinkage is seen when using Cerrosafe alloy to make bore or chamber casts. Cerrosafe is an alloy of bismuth, lead, tin, and cadmium which melts at under 200 degrees F. As soon as it solidifies, it shrinks slightly allowing it to be easily pushed out of the chamber. Then after an hour, it returns to 100% size, and you then have time to take your measurements. After several more hours, it grows slightly oversize. As I recall, even pure lead shrinks slightly as it cools, which is why mold-makers don't ream bullet molds to exact desired finished diameter.

http://www.csalloys.com/products-cerrosafe-alloy.html

Naturally, Cerrosafe might not shrink enough to slide out of a badly pitted chamber or bore. And if you allowed it to cool completely, it would get quite stuck too. You would have to remelt it to pour it out.

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