The Federal tax on distilled spirits is $13.50/proof gallon. That's one wine gallon at 100 proof. A wine gallon at 107 proof is 1.07 proof gallons. The gov't uses the term "wine gallon" to refer to the quantity we all call a gallon. A case of 12 x 750 ml bottles, is 9 liters which is 2.377 wine gallons. So a case of whiskey bottled at 80 proof is 1.9 PG, and has $25.67 in Federal tax on it. About $2.14 a bottle. A case of 120 proof is 2.85 PG and has $38.51 in tax, so $3.21 a bottle. To be quite honest, distributors seem to get a big piece of the pie.

Once a bottle is withdrawn from bond the tax is due. Federal taxes are due twice a month. I have a certain kind of bond coverage ("withdrawal coverage") that allows me to withdraw product from bond (because it was sold) and pay in the next filing date. I imagine most distilleries have this coverage.

Transfer of a barrel from the storage account to the processing account (ie bottling) occurs completely within bonded premises (otherwise it wouldn't be bottled in bond). There are monthly reports every DSP must file that summarize the activity of what's been produced, what's in storage, and what's been bottled. Certainly if things don't add up, the local TTB agent will be paying a visit to see what's up and find out why there's so many more angels at your DSP as compared to all the others.