I've tried searching the net for a table of sorts but I've drawn a blank.

20-1 will yield a BHN of 10. 16-1 will give about a half point more, but not enough to warrant the use of the extra tin.

Thanks Chargar - that's what I needed.

Alan, go to www.castingstuff.com and look at the tester hardness cross reference page (quite a ways down the opening page). It has what you are looking for.
Doz