Mike I believe the Lee 12 gauge slug mold ,which is designed to fit into a 12 gauge shot cup mic's very close to 16 bore size...I took a quick look at mine (which will slide easily into a 16 gauge hull)and it will almost push into my 16 bore Husky rolling block rifle with thumb pressure.
With that being said,I have NOT officially measured them yet,and it would be wise to do so as I'm sure you're well aware.
I would love to hear how you make out with this,mine's a long way from shooting just yet .
I'm so sorry,I just re-read your post ,I did see one at NIE molds I think,and Peter Dyson has just what you're looking for
Last edited by Newf; 02/04/13 08:13 PM.