This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
The classic Estes, Quest and MRC 6 volt launch systems will not reliably
ignite the Copperhead (TM) igniters that come with Aerotech motors, and
Estes Solar Igniters (TM) will not ignite a composite. These motors need
12 volt systems for reliable ignition.