I tried the Ziplock Rolling Pin method on coriander. Man was I pooped afterwards. I found it best to use the handle of the rolling pin like a hammer.
If you need help cracking your grains, you should try to find that dude, Jimmy. From what I heard, Jimmy crack corn, but I don't care.
I use a mortel and pestle to crack coriander, and it is still a pain. I wonder how long it would take to crack enough grain for an all-grain batch with a small mortel and pestle... It would take the patience of a monk.