Grease Gun Has Me Stumped !

I just picked up a small grease gun at a house sale. It seems to be full of grease, but when I pump it, nothing comes out. I also can't figure out how to open it, to see what kind of cartridge it uses. (It's not the standard size.) The part that holds grease (I can't even tell if there's a cartridge in there) is about 6" long.

Such a simple little thing but I'm stumped. Any ideas?

(.-.)

Grease Gun Has Me Stumped !