Really Need Some Help

[Twud]

I've been reloading for factory chambers for 20 years, but never a custom chamber.
I recently ordered a 6MM BR varmint rifle from a local BR gunsmith. I've upgraded most of my reloading gear to the best I can find.
Before he left for Fla. last fall he gave me dimensions for neck turning the Lapua brass I bought. He's not back from Fla. yet and I'm stuck.

Barrel Neck Chamber - .265
Loaded Case Neck Chamber - .263
Redding Neck Bushing - .261
Nech Wall Thickness - .013

I know I've got to take them down in 2 passes, question is where do I want to wind up?

 

[La_man]

Your neck wall thickness is off some.
.013 + .013 = .026 + .243 gives you a loaded round neck diameter of .269, .004 larger than your chamber.
You need to measure the exact bullet you will be using,subtract that number from the loaded neck chamber .2630, divide that remainder by 2 and that will be your required neck wall thickness. Turn a case, seat a bullet and then measure the neck at the base of the bullet with a micrometer to show excactly where you are at then adjust your turner accordingly. Safety and accuracy require that you get these numbers right.