When I set up to size the parent cases 30-30's down to 7mm for my 7x30 Waters I use the same technique. I have however found that if I use one case to set the dies so the case is a "just fit", that the next couple of case may or may not allow the action to close. I was also told by a couple of folks who also had this caliber that what you actuall want is a case which will just allow the action to be closed with just a touch of pressure. In other words a very slight crush on the case. This would be where your action will just about close on the case, but you have to give a touch of help to actually get it there.
My suggestion is to set up the die with one case, then size a couple of more down in stroke, and then try the first time sized to see how it compares to the initial case. Sometimes the case necks will spring back initially and give you a bit different size. If you have it set so that a new case sized with one stroke, will just allow you to close the action, then you should be good to go.
I also do NOT go along with seating the bullets out long and into the lands for fire form loads. This can give you excessive pressure on a not so hardy action. It's much better to simply use a medium rate powder with a bit heavier bullet weight or the cream of wheat method, which I never liked. I found that in most cases the fire form loads out of all of my barrels were usually just as accurate as my handloads. In fact my with .223 AI barrel using the Win factory Varmint Pack loads, I have not even began to duplicate the accuracy or velocity I get from them with similar weight bullets, so I just shoot the factory.
