With the exception of 3⁄32" pyrotechnic safety fuse for use in small arms, must black powder fuses generally be stored in approved explosives magazines?

Yes. Generally igniter fuses, time fuses, blasting fuses, safety fuses, or other black powder fuses by whatever name known, must be stored in approved magazines.  3⁄32" and other external burning pyrotechnic hobby fuses are exempt from the requirements of Federal explosives laws and regulations only when designed for use in small arms. [18 U.S.C. 845(a)(4–5); 27 CFR 555.11: definition of “ammunition”, 555.141(a)(4), 555.141(b)]
Last Reviewed October 4, 2018