Neck turning

[WSM264]

Hopefully sometime this year my gunsmith will get done with a 6-284 project that he has had for 3 years.  I am necking down WW 284 brass to 6.5 then 6mm.  How thick should the neck wall thickness be??  I was told .015" put I don't know if that is per wall or total. 
If my newly formed brass is .240" on the inside of the neck, should the outside be .255" or .270"?

[jedman]

  I wouldnt turn it until you get your gun back to see what size neck your gun has.
I had a 98 Mauser in 6 X 284 that had a tight neck and showed pressure signs way before full loads were ever got to.
I just didnt know what to look for back then, best to have a minimum of .002 clearance over the loaded size of your cartridges.                    Jed

[LaOtto222]

I like snug necks, I think it makes for the best accuracy. However, as jedman has pointed out, you can get them too tight. I agree with jedman, .002" is about right for clearance between a loaded round and the reamed neck size. To be sure take a chamber cast and measure your chamber. Then measure the case neck thickness X 2 and add in the bullet diameter. It should be .002" less than your chamber cast. If it is too large, then turn your necks down to match. If you waited for three years, waiting a couple of more months to get it right is not that painful.

Good Shooting And Good Luck.