Unclenick -
Thanks very much for the detailed info. I found a program called WinLoad by John Knight in the UK -
http://www.stickledown.co.uk/ - that does say that it's based on the algorithms developed by Powley. I downloaded it and tried it, but as you say it looks like it's only applicable to a narrow range of cases for IMR powders.
As I would like to understand the relationships better between the parameters (making small changes in established loads) it looks as if QuickLoad is going to be the way to go.