Section 4221(a) of the Code applies only in those cases where the exportation or use referred to is to occur before any other use, and where the seller, first purchaser, and second purchaser, as may be appropriate, have registered as required under section 4222 of the Code and paragraph (a) of §53.140. See paragraph (c) of this section for provisions relating to evidence required in support of tax-free sales. See §53.141 for exceptions to the requirement for registration. Where tax is paid on the sale of an article, but the article is used or resold for use for an exempt purpose, a claim for credit or refund may be filed in accordance with and to the extent provided in sections 6402(a) and 6416 of the Code, and the regulations thereunder (§§53.161 and 53.171-53.186).
27 C.F.R. § 53.131