In Egytology, scarabs are often referred to as having a "cartouche." This word is from the French, meaning a roll, or more correctly, a scroll, or paper. Advertising of the mid-ninteenth century often depicted a scroll partially unrolled bearing the advertiser's logo or monogram. So, cartouche became to mean a roll of paper.
Now.......... early cap-n-ball guns were slow to load, measuring out the powder from a powder horn and all. So, someone came up with the idea of placing a pre-measured powder charge inot a roll of paper, skin, or foil. At one end of the roll was the bullet. The roll was torn open, the powder dumped into the barrel, then the bullet was seated with the short starter and then the ram-rod.
With the coming of the Colt revolver, the roll was combustible paper, glued to the base of the bullet. The whole cartouche could be loaded into the front of the cylinder without tearing it open.
So, in the course of time, "cartouche" became "cartridge."