i tried diferent approaches but the best so far is i used a redding body die in 6.5 cm then trimmed to 6.5cm thength then ran them thru a f/l cm sizing die checked to make sure they would chamber i in my rifle(had to run them through the body die again).then expanded the necks with a sinclairs expander . i measured a fired case to get a basis on my rifles chamber ,loaded up a dummy round to see what a loaded round measured and found that to get a .002-.003 clearance (loaded round ) i needed the cases to be .0145 thick measured with a insize digital thickness guage .i set my neck turner with a set of feeler guages from the auto parts store and did a few test runs i cut slightly into the shoulder to get any doughnuts out then run them thru the case trimmer again to make sure they are to correct legnth.
i still need to fire form to my chamber i'm going to use a min. charge and work up a load since these are lake city lr brass i'm using and are thicker then hornady's brass. i'm getting ready try it out on some 308 lapua bass next then see what the difference there is in fps between hornady,lc,and lapua in the end all i'm looking for is a better case life i was only getting 2-3 reloading out of hornday brass and thats not exceptable to me being i'm on 20-25 with my lapua brass (i use a bushing neck die and only f/l when needed i also anneal every 4-5 firings ).
hope this helps i know there are more on here that might have a better way to do things than me i'm still new to neck turning myself there is alot of talk over at 6.5 creedmoor.com they have helped me out alot in this .