27 CFR §479.61

Except as provided in this subpart, there shall be levied, collected, and paid upon the making of a firearm a tax at the rate of $200 for each firearm made. This tax shall be paid by the person making the firearm. Payment of the tax on the making of a firearm shall be represented by a $200 adhesive stamp bearing the words “National Firearms Act.” The stamps are maintained by the Director.