27 CFR §19.227

After gauging, the proprietor must determine the tax on the spirits to be removed from the bonded premises. The proprietor must use the tax rate prescribed in 26 U.S.C. 5001 to calculate the tax, unless the product is eligible for a reduced effective tax rate as provided in 26 U.S.C. 5010. If the product is eligible for a reduced effective tax rate, the proprietor may use that rate to determine the tax. The proprietor must record the results of each tax determination in a record of tax determination as required by § 19.611.