27 CFR § 19.249 - Average effective tax rate.
(a) Establishing an average tax rate. The proprietor may establish an average effective tax rate for any eligible distilled spirits product based on the total proof gallons in all batches of the same composition which have been produced during the preceding 6-month period and which have been or will be bottled or packaged, in whole or in part, for domestic consumption. At the beginning of each month, the proprietor must recompute the average effective tax rate so as to include only the immediately preceding 6-month period. The proprietor must show the average tax rate established for a product in the record of average effective tax rates as prescribed in § 19.613.
(b) TTB review of average effective tax rates. If the appropriate TTB officer finds that the use of this procedure jeopardizes the revenue, or causes administrative difficulty, the proprietor upon notification from TTB must discontinue use of this procedure.