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wncchester · September 26, 2012, 08:55 AM

"What is the process to determine how much to turn necks down and how do I measure the brass?"

"The" process is whatever you wish, there's nothing established about it and what we wish varies quite a bit.

Case necks tend to be much thinner than they need to be for a standard chamber so any turning we do just makes a bad fit worse. Most of us want to avoid excessive thinning so we generally skim off an average of maybe 75% of the circumference and call that good.

We can measure neck thickness at the mouth with the jaw tips of an inexpensive dial caliper OR buy a much more costly "ball mic" micrometer. Or seat a known diameter bullet and mic the outside diameter of the neck that way. Actually, since neck thickness is not at all critical for factory chambers I no longer bother to measure turned necks. Well, except for massive case conversions or tight neck chambers that require turning to allow chambering but those are not common things.

Case brass can only stretch about 1 thou before the metal's elastic limit is exceeded. Knowing that allows us to mic the diameter of a fired case neck and add a thou and be reasonably sure that's the diameter of the chamber's neck. (It also tells us that any so called "neck tension" greater than a thou is kidding ourselves so far as bullet grip goes.)

September 26, 2012, 08:55 AM	#3
wncchester Senior Member Join Date: December 1, 2002 Posts: 2,832	"What is the process to determine how much to turn necks down and how do I measure the brass?" "The" process is whatever you wish, there's nothing established about it and what we wish varies quite a bit. Case necks tend to be much thinner than they need to be for a standard chamber so any turning we do just makes a bad fit worse. Most of us want to avoid excessive thinning so we generally skim off an average of maybe 75% of the circumference and call that good. We can measure neck thickness at the mouth with the jaw tips of an inexpensive dial caliper OR buy a much more costly "ball mic" micrometer. Or seat a known diameter bullet and mic the outside diameter of the neck that way. Actually, since neck thickness is not at all critical for factory chambers I no longer bother to measure turned necks. Well, except for massive case conversions or tight neck chambers that require turning to allow chambering but those are not common things. Case brass can only stretch about 1 thou before the metal's elastic limit is exceeded. Knowing that allows us to mic the diameter of a fired case neck and add a thou and be reasonably sure that's the diameter of the chamber's neck. (It also tells us that any so called "neck tension" greater than a thou is kidding ourselves so far as bullet grip goes.)