The Neimiller is simply a .243 Winchester with the shoulder pushed back .1".  In my case, I already have a properly chambered .243 barrel that I'll have a machinist take .1 off the breechface.  I'll cut the neck of the chamber forward that same .1.  All I need for a die is a .243 die with .1" taken off the bottom.  I'm going with a rimmed case for function, found some 6.5x57 rimmed that will be the parent case.  The rim is a bit smaller than a Krag rim @.520", but should still work.  Biggest reason for decreasing the length to shoulder of the chamber is to keep someone from using .243 in it.  I have had 6mm/30-40AI reamer and dies for years now, but with the already chambered.243 Win barrel I recently got, the Niemiller seems to be the way to go.

I guess Sedgley thought the file test told him something.