H
The bag charge bins did indeed have glass fibre jackets around them which were charged at pressure with coolant, very handy for keeping yer Paderborner pils cool on exercise ;-)
As regards the vent tubes, Chieftain main armament ammo was in two pieces, the projectile and the charge. This cuts down on turret clutter as there is no brass case to dispose of as the charge incinerates totally in the breech. The bag charge needs igniting and the easiest and safest method at the time was by using a vent tube which in effect is an electrically fired ballistite brass cartridge. This ignites the primer pad at the rear of the bag charge which in turn ignites the cordite propellant, the resulting explosion propelling the projectile down the barrel etc.... The vent tubes were held in a magazine at the rear of and underneath the breech ring. The main draw back in the early marks was that each vent tube had to be manually rammed utilising the vent tube loader and in the correct loading sequence for each round fired. They were also prone to not 'firing' due to electrical failure or, very rarely, faulty manufacture.
Regards
Graham