Sorry to hear of your problem. I just checked mine, and every one in my kit measures within .004" of each other, the thickest being .250". It looks as though there is about .030" more clearance in the slot on the tool, allowing them to go to .280", if nesessary. If it was me, assuming you have the correct type shellholder, I'd simply file down the bottom a few thousandths, until it fits. By design, it won't hurt anything. Granted, you shouldn't have to do this, but it would work, in a pinch. Otherwise, send it back to Lee, I'm sure they'll make it right.
Hope this helps,
MH