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I use all grain does good and good taste but can't get it to go above 100 proof

thanks for letting me join here hope to one day to be as good as my dad at this .I do have one problem with the way I do it but it is good .I have a 8 gallon copper still with a 1/2 gallon thumper run in to a worm but can't get it to go above 100 proof when it starts good taste and blue flame good s...