I found this cartridge and I'm curious about it. The marking on the bottom is "MTY" and "66". It had no powder in it when the bullet was pulled but had something weird. It almost looks like there is another brasstory piece pushed in there that contains powder?
Bogwalker has a picture of a SMAW cartridge in the cartridge collector thread along with a nice description of what they are used for. It is a spotting round.