The CHIRON2 rocket requires custom made casting tubes. As the kraft paper tubes of the CHIRON1 rocket may have caused the engine failure, a more solid approach was taken.
120*114 (OD/ID) aluminium tubes were reduced to approximately 117.5*114. To assure proper bonding of the sorbitol propellant, a single layer of thick kraft paper was glued into the aluminium tube.
Fig. 1. Aluminium tubes with the inner layer glued in.