You have to love it when a US Court of Appeals has the following to say to the ATF on the subject of their jihad to regulate the model rocketry hobby out of existence:
The problem in this case is that ATFE's explanation for its determination that APCP deflagrates lacks any coherence. We therefore owe no deference to ATFE's purported expertise because we cannot discern it. ATFE has neither laid out a concrete standard for classifying materials along the burn-deflagrate-detonate continuum, nor offered data specific to the burn speed of APCP when used for its 'common or primary purpose.' On this record, the agency's decision cannot withstand judicial review.
You can get the full story from the guys who beat them, the National Association of Rocketry, here. Nice work, guys.