I've passed stones that were 1 cm but I used the epsom salts (ES). If something gets stuck just take another dose of the ES. They say you should wait 2 weeks inbetween flushes so that the stones from the back of the liver roll forward to come out next time.
You should read some of hopinso's posts. She has gotten some really big ones out with the ES. Shellycat can't use the ES and takes herbs to dissolve the stones first. So she only gets sludge, I'm guessing. Click on Shellycat's posts for lots of imformative info. And Flowergirl is quite experienced as well. They will probably all get back to you.