I found this page
which says they're 73% "sugar", 23% glucose, and about 4.2 g apiece. If the "sugar" is sucrose and those are weight fractions, that's the equivalent of 4.0 g of sucrose. Which adds about 3.0 vol to a 12 oz bottle - so around 3.9 vol total.
Even if the "sugar" is another monosaccharide, it's adding about 2.8 vol. So at least one of those numbers has to be wrong. Or they're going to be hugely carbonated.