I don't think anyone has dosage amounts on the magnesium citrate for the actual flush but I have noticed that when I take a little extra on a daily basis I can sometimes feel the relaxing of the ducts.. i.e. a little twinged of dull pain. Probably a few stones lining up. I personally like Mg Citrate as the citrate converts to bicarbonate in the body and as I mentioned in a previous post causes a more forced contraction of the gallbladder (at least according to one study.)
I still think Espon salt is better for flushing though as it is a proven winner.