I want to correct the misconception stated above concerning hazmat fees.
All rocket motors are considered hazmat for transportation by DOT. If you use any commercial carrier for a hazmat shipment, the shipper can be, and almost always is, charged a $20 hazmat fee by the carrier for a hazmat shipment to cover the extra paperwork and handling costs of the shipment, and 99% of the time it's passed on to customer. (UPS, Fedex, Yellow Freight, etc. are examples of common carriers. Not all common carriers accept rocket motor either.)
The US Postal Service, as a government agency, is exempt from DOT regulations, but they do not accept hazmat shipments of any kind so you will never be charged a hazmat fee by the Post Ofice. By a USPS ruling, rocket motors containing not more than 30 grams of propellant are declared non-hazardous for Parcel Post shipment within the Post Office system provided they are properly labeled and packaged. Many AT mod roc reloads are ok for the manufacturer and their distributors to ship by USPS, but some aren't. The motors that can be legally shipped by USPS without a hazmat charge are listed in the AT document I previously posted. AT is in the process of changing most of their single grain F and G reloads to a two grain design that meet the 30 gram requirement, but there are still a lot of older reloads out there. Their new loadable line is a legal way around shipping single use G-motors by USPS because each of the propellant grains do not weight more than 30 grams.
For the new folks here, I will repeat there are big fines for not declaring and/or improperly shipping rocket motors or any other hazmat. For a company the DOT fine is typically $30,000 for the first time you get caught shipping undeclared hazmat, and for an individual several thousand dollars. Do it a second time, and you're probably looking at jail time. The odds of getting caught are relatively low, but if you are caught, the penalties are severe.
Bob