What is the minimum clearance one should have between loaded case neck diameter vs. chamber neck diameter?

ANY clearance is enough. In a hunting rifle about .004" is sufficient to insure bullet release even if debris and carbon exists on either the case or in the chamber, however, if you like to live dangerously, .002" is OK. Benchrest chambers measure clearance in the tight necked chambers in the .0000".

"Benchrest chambers measure clearance in the tight necked chambers in the .0000". "

But no crimp, please. If a crimped neck will fit the chamber without play,there is no space for the brass to release the bullet and pressure my increase dangerously.

What Bob338 and waitaminute said is also what I've learned.

For BR rifles with fitted necks that require little or no neck sizing between firings, total clearance is measured in the .0000" or ten thousandths... neck turning required.

For minimal neck sizing that most tight chambered BR rifles have went back to, total clearance is .0015" - .002" and need necks turned as well.

.004" total clearance is a good "tighter neck" than factory, that should work well. Better than the .006" - .010" clearance factory stuff gives by far.

I make no claims to knowing anything about BR minimum chambers. BUT, in a hunting weapon in which you want optimum ballistic performance, if the fired cartridge's neck WILL NOT PERMIT you to drop a bullet through it into the case, the clearance is NOT SUFFICIENT for safety!!

A little slop may not be a bad thing. I went to Harts for a new 26" SS barrel for my .22-250Rem. I asked about the neck diameter, and the smith told me .258". I thought this strange since .224 + 11 (twice) gives me a loaded round of .246". That's an extra 012". I asked if that wasn't excessive. He simply said no. Well sir, that bloody rifle might weigh 13lbs., but it steadily shoots 5 shot, 100yd. groups in the mid .2"s. I'm happy as hell, and am a little slower to question these things now. Go figure! Best wishes.

Cal - Montreal

Cal,
I think it only comes down to how much you want to work the brass, that's about it too, .012" is larger than any of my factory chambers clearance and is IMHO quite excessive. Can't argue with how yours shoots though, nor would I. If you keep headspace short and tight it will always center off the shoulder anyway, if it's loose, well, that's a different story now.