We need to review the TARC Engine List to be sure we are within the rules.

We need enough total impulse to raise our rocket to 850ft.  Last year we found that an Estes E9 motor could get to 850 ft if the weight of the rocket was around 270 grams.  The E9 has a total impulse of 28.5 N-sec. The E9 comes with 4, 6, and 8 second ejection charge delays, but we know through experience these can vary as much as a second or more.
Our designs are leading to a rocket over 280 grams, so we will need more than an E9.  But the E9 is the largest of the Estes black powder motors.  We will need to use an Aerotech composite motor.  Aerotech makes an E15 that has a total impulse of 40 N-sec.  That may work.  It is a 24mm diameter motor.  We may have to go to an F motor. 

Aerotech makes both single use motors and reloadable motors.  Single use motors are easier to use and perhaps more reliable, but the reloadables will save expenses. The only 22mm F single use motors (F21) are very hard to get.
The reload kits are about half the cost of the single use motors. The reloadable motor systems (RMS) require a cylinder that is purchased once and used may times.  You need to use it 7 times to break even with the single use motors.

There is an F24 reloadable that looks promising.  There is also an F12 that might work better with our rounded nose cones (higher drag).

You will need to spend time cleaning out the reloadable hardware right after the launch.  Here is a cleaning procedure.

Check out the Aerotech catalog to get all the information on the Aerotech motors.
 

Here is a thrust chart for the E15W and E30W. They come with a 4 or 7 second ejection charge delays. They weigh about 48g.

Here is a thrust chart for the E18W. It comes with a 4 or 7 second ejection charge delays.  It is close to an E15W. They weight about 58g.

Here is a view of a reloadable engine.  We need to develop our skill loading these things.

Another New Idea

In order to get a bit more from our E9, we would like to try a piston assist as documented at http://members.aol.com/petealway/piston.htm. Maybe we do this next year.