To legally ship rocket motor of any size, one must obtain an EX number for your propellants after appropriate third party testing to insure that the motors meet DOT shipping requirements. For whatever reason, the owner of US Rockets did not do this nor did he possess a required BATFE Explosives Manufacturing permit. He was caught shipping his rocket motors deliberately mislabeled as model air plane parts without any hazmat permits, hazmat labeling and packaging or documentation. He was convicted of a felony and heavily fined. I do not know if he served any jail time, however he was certainly eligible for it.
Prior to this event, US Rockets had submitted some hobby rocket motors for certification, and I believe a small number were certified. The certifications were withdrawn based on the conviction and the lack of valid documentation for the EX numbers.
Bob