Sizing rifle brass to chamber.

Why is chambering freely the goal? An inability to close the bolt would be something to avoid, but what is it about smooth cycling that indicates a better fit than a little resistance?

I can see how sizing 1 to 2 thou under the dimension of a once-fired case could be needlessly sizing the case down, and the bolt close method would disclose whether the case really needs to be sized down that much or not. Bumping a fired case seems less and less likely to size the case down excessively on subsequent firings. Even so, I can see how the bolt-close method could be used without the necessity of more firings and that it demonstrates a more direct feedback.

 

I haven’t had my coffee yet so this could be the dumbest post ever or might make sense. The standard difference in length between a go and no go is .004 same as the body reduction of a standard die vs finish reamer, our “match” dies hopefully are minus.002 body reduction. Shoulder bump or creating headspace can be increased or decreased by way of threads, shell holders or milling an extra few thousands off the bottom as with Redding type S (speedy) bushing dies. The gag is who speced the reamer that was used to chamber your barrel and can you get a copy of the reamer print to order a die? If not it’s trial and error with a few options where most guys do the trial and error you read about on line.
Anyway here is a shop tolerance sheet from one of top companies who make reamers.

 

(Free chambering means smooth cycling, no one wants to fight a bolt open during hunting season or in battle not to mention during competition.
Galling the bolt lugs can be an additional outcome from excess resistance during bolt manipulation.)
I use a farm boy sketch when setting up dies and measuring body reductions, headspace etc.

 

Fair clarification: Bolt lift method just finds the headspace length of the chamber - the loader then has the option of choosing whatever shoulder bump, whatever clearance, they want from there.