Thank you. I did a little research and saw where that one company was bragging about their 8 sec. burn. Too intense. I suppose the experimental fuels are frowned upon. What about high carbon black powder? Would that be mellower?
I wouldn't say too intense really...it works just fine for 1.5m span gliders that are built stupendously light. A friend of mine put an I motor into a highly modified (bagged in carbon) Estes Stratoblaster and went about 350 mph with it. Burn time is like 0.75 second for that setup.
I highly discourage custom propellant mixes for newbies. It can and has been done, and works well under controlled conditions, but you can cost yourself a lot of money and possibly get hurt badly if you do it wrong. And there are a lot of ways to do it wrong.
No ideas on longer burn motors. Not my specialty by a long shot. The guy who makes the Rapier motors had it down for the most part, but they're now export restricted from the Czech Rep, and there was a period where they were experiencing catastrophic casing failures from grain delams. Not particularly dangerous, but a good way to destroy an expensive airplane.
With that in mind, Aerotech bragging about an 8 second burn seems justified. Long burns are tough. They like to explode.