Chamber dimension, freebore -> 300PRC / Hornady ATip 250

If you are not constrained by magazine length, you generally want the junction of the boattail and the bearing surface to be seated to the depth of the neck, shoulder junction. That way, the projectile is fully supported in the neck, but not seated any deeper than that and unnecessarily taking up case volume.

If you want to make sure that it will chamber at whatever length that measurement comes out to be, you have to send it to a reamer maker and have a custom reamer made with whatever free bore you want on top of that length, or you have your gunsmith extend the free bore after chambering it with a standard reamer.
 
hmmm, ok, but would we not rather want a tight fit... that implies less expansion during firing, aka more stable, less stress on brass.

My understanding is with a SAMMI chamber, there is not enough room for the brass to expand then spring back. Then there are sizing dies that don't size the brass small enough. Google Alex Wheeler. He has really good videos on his web site.
 
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And in my experience, there is not hard bolt lift like over pressure. At the top of the bolt lift your bolt handle hits the primary extraction. The click happens when the case pops loose and the handle hits the receiver.