Is Bullet Weight Shrinkage a Factor of Casting Temperature?

[John Boy]

... or asked another way - can the weight of a cast bullet be increased by varying the temperature of the melt?

Background:
I have a 38-55 mold that was designed to have a nominal weight of 330gr using 1:20 alloy. I have cast them with 1:20 and 1:30. The weights at 1:20 are 317grs (680 degree melt) and the weights at 1:30 are 326gr.

I have varied the temperature casting the 1:30 alloy from 720 to 780 degrees. While casting at 760 degrees, I had only one perferctly formed bullet drop at 329grs while the rest were 326.0 to 326.7grs with less than 10% outside the bell curve

So, the question is: to obtain heavier weights, which way should the melt temperature go - Up or Down to obtain a heavier weight bullet?
Do know that:
*** soft alloy bullets for a .375 diameter shrink .004 and harder alloys shrink less. But this bullet is used with original powder not nitro in the velocity range of 1040 to 1080 fps. Need the soft alloy for obturation
*** I can 'Beagle' the mold and the weight will increase because of the increased diameter of the bullet. But would like to get this mold to cast 'as is'

Thanks for looking and possible advice

[leftiye]

If you raise temp, the mold expands. The cavity expands too. But being hotter the lead shrinks more too. So you'll have to experiment to see where there is a weight gain. Unless I'm deluded, frosting (hot mold and/or melt too hot) results in weight loss a little, so too hot may not work. This is probly moot with pure lead, as only alloys with antimony form crystals.

IMHO, it may be more important to get good fillout (make more difference in weight). Low alloys (nearer to pure lead) shrink less, and make heavier boolits, FWIW. Add a little tin to help fillout. Most of the time you have to cast very hot to get good fillout with pure lead as it doesn't melt at as low of temperatures as alloys do.