I agree. I haven't done this myself yet but I have a friend who has worked up a load in the same cartridge but in an older "non-adjustment screw" Merkel. He ended up coming up with a load that was already listed in Graeme's book. Next time he'll reference Graeme's book first (as will I). Use one of Graeme's listed loads and then adjust the barrel to suit.

I've used Graeme's loads in my 500NE Merkel and the regulation was excellent