M style expander for Star machine

A couple of questions came up after I posted on another thread about using an M style 2 step expander ball on my star machines.  The first was what size 2nd stage diameter for particular bullets. I settled on two thousandths larger than the bullet diameter.  Having tried one thousandth larger I found it was too much of a struggle to slide the bullet down, I use Nosler jacketed which seem to run slightly larger than .451.  I have no knowledge of what Zero bullets run.  The second question that I was asked was where the dies came from.  I got a set of three dies- .448/.452, .449/.453 and .450/.454 from LSP (Lebanon Screw Products) in Windsor, Vt.  I was advised that they are made from A2 steel and hardened to 55 Rockwell. They run about the same price as original Star belling expander dies.