Gas generating compositions having a fuel preferably comprising a mixture of 5-aminotetrazole (5-AT), azodicarbonamide (ADCA), an oxidizer, and a superfine metal powder burn rate enhancer such as nano-aluminum, for use in automotive seatbelt pretensioners and other suitable applications requiring high impetus, high rate of gas generation. Also, methods of making these compositions, and devices incorporating them such as seatbelt pretensioners.