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Old August 20, 2013, 02:14 PM   #26
totaldla
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Pardon my naivety, but doesn't neck-sizing remove all this concern over head-space? Assuming the cartridge case doesn't separate on 1st firing, wouldn't the newly fire-formed case have "perfect" head space?
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Old August 20, 2013, 02:21 PM   #27
dmazur
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To a point, yes.

But nothing is perfect, and the chamber/bolt system is elastic to some degree.

Even those who expound on the virtues of neck sizing will admit, if their feet are held to a fire, that they have to full-length resize occasionally.

And if you use neck sizing for a gas-operated rifle, sooner or later you will encounter chambering difficulty. Neck sizing also increases the risks of experiencing a slam-fire in these rifles.
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Old August 20, 2013, 04:38 PM   #28
mehavey
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Quote:
Pardon my naivety, but doesn't neck-sizing remove all this concern over head-space?
Assuming the cartridge case doesn't separate on 1st firing, wouldn't the newly fire-formed
case have "perfect" head space?
For a short period (3-4 firings) yes. Case growth still occurs just from brass flow,
however, and eventually the shoulder will again be an interference fit -- and require
resizing again. (It's why Redding still ships an FL resizing die with all it's full-up
competition/neck die sets.)
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Old August 20, 2013, 10:07 PM   #29
Bart B.
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Neck only sizing fired bottleneck cases typically doesn't center the sized neck perfectly centered on the shoulder. Nothing holds the case body and shoulder in place while the case neck's sized down. Which is why most benchresters have lately switched over to full lenght sizing their fired cases. Read the section in the following link about sizing 6PPC cases, the part titled "Custom Dies Work Best:"

http://www.6mmbr.com/6ppc.html

Bottleneck cases headspacing on their shoulders get driven hard into chamber shoulders a few microseconds before they fire. At that time, the case shoulder's perfectly centered in the chamber shoulder. That's when one wants the case neck to also be perfectly centered in the chamber neck.

It's fairly easy to control sized case headspace, especially with Redding's competition shell holders that come in .002" height steps. Use the one that lets your full length sizing die bump the fired case shoulder back .001" too .002" (as measured with the right gauge) when the shell holder stops against the die's bottom as the press handle cams over. Done right, your cases will have a very small spread in headspace. It doesn't matter a whole lot anyway as their front end centers perfectly when fired. Head clearance may vary a bit; the space between the bolt face and case head. That's not a big issue as long as it's not more than.003" max which gives long case life and great accuracy.
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Old August 22, 2013, 06:41 AM   #30
F. Guffey
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“It's fairly easy to control sized case headspace” SAAMI does not list case head space. SAAMI list the case as having a length that is measured from the datum/shoulder to the head of the case. SAAMI does list the chamber as having ‘head space’.

I dug back in time to 1958, glossary of terms, head space, no mention of a case having head space. Now? I notice the statement “some people call the distance/length of the case from the shoulder/datum to the head of the case head space” I noticed L.E. Wilson named their case gage CASE GAGE, a gage built so well most reloaders can not appreciate it for its accuracy. Then there are comparators, also referred to as head space gages, The up side? If a reloader is lead to believe a comparator is a head space gage and the comparator is listed as a head space gage getting their money should be easy. Why?

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