Ah... I left something out.

I build my cones from 110 lb card stock, and add several "Longerons" lengthwise aft of the bulkhead.

I fly simple cones based on my glider cones sometimes. I have had one collapse due to wind-force and Krushnik effect. Once I added the longerons, I had no more troubles - even when launching on "D" motors.

The longerons themselves are strips of 110lb card stock folded to look like this when seen from the end "_/\_". They add rigidity and move the CG aft (a TWO-FER!).

__________________
John Adams
"There is a lot of rocketry under 20ns"