It is a LEE mold in .540 diameter which should by all indications fit the .54 caliber. They do work, the whole point is they could be just a hair tighter. The 380 grain LEE R.E.A.L. conicals are the same diameter and they work just fine, but they "rifling engaged at loading" as the name implies. Minnies on the other hand engage the rifling when fired. This was done so they could be loaded in dirty fowled barrels under battle conditions easy. (From what I have read)