With muzzle loaders there is blowback through the nipples or touch/flash hole The self contained cartridge seals off the breech and for all practical purposes stops fouling migration. It's really simple and a great improvement over muzzle loading technology. Guy's it really is that simple. With a heavy shooting season using my cap and ball revolvers at the end of the season I'll clean the internals and apply a coat of oil then reassemble. Any powder fouling that gets into the action lands on top of the oil part and no corrosion. If using lightly I can go a few years and still not have any problems.
