10 U.S.C. § 2385
Arms and ammunition: immunity from taxation
No tax on the sale or transfer of firearms, pistols, revolvers, shells, or cartridges may be imposed on such articles when bought with funds appropriated for a military department.
No tax on the sale or transfer of firearms, pistols, revolvers, shells, or cartridges may be imposed on such articles when bought with funds appropriated for a military department.