The reason for the different shapes is because of the length of the primer in the cartridge case. Number 1 is packed around the primer. Then numbers 2 to 6 are packed to the side of the primer and number 7 sits on top of the primer, just beneath the base of the projectile. The rusty looking bags are designed for firing with the older model of 105mm...mostly used in WW2. This cartridge case used a much shorter primer and the bags used were more uniform in shape... as can be seen. They were stacked on top of the primer with sometimes the bottom one being secured by a bronze clip, which often left the barrel with the projectile. Sorry, I just have to say it...."the ones marked INERT only are for firing INERT projectiles" ?????? If they are inert they can't be fired at all. Surely..... They are in reality for use in either DRILL rounds or for display pieces, classroom instruction etc. The unwanted bags are left out of the case when the complete round is on the loading tray, but still attached by their string. The Number 1 of the gun is responsible for checking the correct number of bags being used and then pulls and breaks the string and discards the unused bags for later destruction.