Used Estes C6-3; and it rose up beautifully.  Arced over a bit and after apogee the charge blew the rocket apart.  I had made sure with a poke test that the parachute wasn't too tight, but the charge made the rocket come down in 5 pieces (nose, parachute, body, motor, motor retaining ring).  I think it was a certain lot of C6s I had (from Estes Blast Off Flight Pack) with too much ejection charge.  Broke a body fin on landing, but will fly again...maybe after some modifications.