Can you post some pictures of the de lamination ? A couple things that help me are cleaning the stock really really well, to remove all oxidation I scrub with dawn dish soap/ hot water with a white 3m scotchbrite pad then wearing nirtile gloves I wash again with acetone before stacking the billet. The other thing is to make sure all the pieces are cut clean and square with no waves or fish-hooks at the edges, any voids in the edges tend to be a spot for a de-lam failure to begin. I did try the stacked coin thing a few times with some success but have better luck with new, clean nickle silver, copper & brass. I haven't been brave or rich enough to try gold or silver yet.