Re: reamer dimension for 6.5/284
yes the neck diameter is important but that is can easily be adjusted with a good neck turner.
The biggest problem between the Win and Norma brass is the case head diameter not the neck diameter. I believe the Norma brass runs a .001 or .002 larger. So if your reamer/chamber was cut based on Winchster brass dimensions the Norma brass won't fit into your chamber. I don't own a 6.5-284 but shoot with enough guys that do that this is a fairly well known "problem". I would hve to double check to maake sure that it's the Win brass that is bigger. Don't quote me, jsut be aware there is a difference. Don't know how the new Lapua 6.5-284 measures yet though. Also Hornady is making this brass to give you another option.
hope this helps,