Can temp affect weight of bullets?

[fiatdad]

I was casting 180 lee .30 cal bullets the other day. I did it in two sessions, the first I ram the temp hotter and at a quick pace. The other was cooler and a but slower. The weigh variance between bullets in each group ran 1 grain but the variance between the 2 groups was 3 grains. The first ran 178.9 to 179.9 the second was 176 to 178. how could this be?
thanks Nick

[StuBach]

Has to do with the expansion of the alloy due to heat I believe (though I’m no metallurgist). Depending on the alloy the effect may be more pronounced but I’ve noticed that when I run hot and run just on the edge of frosty bullets I get slightly heavier bullets but when I run cooler going for mirror finish I get slightly lighter.

[charlie b]

Two parts. Heat of mold means mold is different size. Heat of alloy means it will be a different density at a different temp (size will be different).

[fiatdad]

Thanks I needed validation on my theories. I realize this happens but the gross difference was more than I expected on small bullets.
I say cast them and let them fight over the jackets
Nick