Edit: I always shoot for 8%, read that early on here somewhere and it stuck with me.
1 cup (166g) yellow corn = ~1.1g sugar
1 gallon = 16 cups (liquid)
The typical weight of feed corn (#2 yellow dent corn) is 56 pounds per bushel. By volume, there is about 8 gallons in a bushel. Thus there is 7 pounds in a gallon of corn.
So, 166 x 16 = 2656g / 1000 = 2.656 kg / 2.2 = 1.2 lb sugar in 7 lb of cracked corn (based on the medical math I do everyday modified for distilling - go figure
7lb cracked corn (1.2 lb. sugar) + 5.6 lb sugar = 6.8 lb. into 6 gallons of water should come up with a wash of 8% and have a specific gravity of 1.052. According to the parent site.
Just musing by me before work.
Edit: this is wrong now that I look at it. Will edit it later on when I get home. Should not math when I wake up