Insulator around delay element burned thru along outer seam spiral. This caused pre-mature firing of ejection charge under thrust, and failure of forward closure threads.
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Motor burned for approximately 1/10 second before failure. It lifted my rocket about 30 inches up a 60 inch 1010 launch rail when the failure occurred. Casing was an Aerotech 29-40/120 reload casing. Only about 5% of the propellant was burnt.