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From: (Bart Bobbit)
Subject: Re: Case neck wall thickness question?
Organization: Hewlett-Packard Fort Collins Site

There really isn't any `standard' neck wall thickness for about any
cartridge.  One thing to consider is that if they're too thin, they
won't last long before splitting.  So, in this regard, the thicker,
the better.

As long as the loaded round neck outside diameter is no less than
0.005-in. smaller than the chamber's neck diameter for standard rifles,
you should be just fine.  The exception is in some benchrest rifles,
loaded round outside neck diameter is about 0.001-in. less than the
chamber neck diameter.

If you outside neck turn all your cases to just barely peel off brass
from the thinnest neck in the lot, you should be just fine.  Keep in
mind that uniforming case necks typically won't show any accuracy
improvement for factory chambers.  Nor will any significant improvement
occur in most 'smithed chambers.  The only time I've seen accuracy
improvement by uniforming neck wall thickness is when a top quality
match barrel is chambered with a top quality match reamer whose pilot
is a perfect fit to the bore diameter.  This allows the chamber's neck
and throat to be perfectly centered on the bore axis.  Uniforming neck
wall thickness definitely helps in these chambers.

Another thing about uniformed neck wall thickness is that the benefits
of such case preparation is typically nulled when conventional sizing
dies are used.  The sizing die (neck or full-length) should NOT use an
expander ball; those things bend case necks enough to mask any accuracy
improvement uniforming neck wall thickness might do.


From: (Bart Bobbitt)
Subject: Re: contender, 10mm, and micrometers
Organization: Hewlett-Packard Fort Collins Site

Kevin Sedota (edsr!kjs@uunet.UU.NET) wrote:

: I want to start turning cases for my 788 in .223.
: I need a tubing micrometer.
: I seem to be having trouble finding them around here
: although I have seen them
: for ~$100. (it's the Mitutoyo). Is this a reasonable price or does someone
: know where I can get them for less. Or is this one of the prices
: you pay for
: accuracy.

You can mic a bullet's diameter, then seat in in a neck-turned case,
finally measuring the outside neck diameter.  One-half the difference
is the neck thickness.

But I doubt if neck turning will improve accuracy.  It will definitely
reduce case life for that factory chamber.  There's a number of other
things that cost less and will improve accuracy a lot more than buying
a tubing mic and neck turning tool.  Besides, neck turning cases, then
running them into, then back out of,  a sizing die with an expander ball
will cause their necks to bend a greater amount than if not turned.
The result is even more crooked ammo; not at all good for accuracy.

If you consider neck wall
uniformity important, I suggest you just use cases with regular necks
that are within .0005-in. of being uniformly thick.  Those cases will
probably shoot more accurately than those with greater errors you turn
to some thickness.


From: (Bart Bobbit)
Subject: Re: [RELOAD] lubing inside of necks (was Re: Questions about reloading 
	and .308)
Organization: Hewlett-Packard Fort Collins Site wrote:

: Bart,

: Do you turn your case necks for uniform thickness?

Only if they have a spread of more than .001-in.  Most of my commercial
cases don't need neck turning.  These include Federal, Winchester Palma,
WCC-58 or WCC-60 match cases, and Remington BR.  My Winchester .30-.338
cases needed to be neck turned; they had about a .002-in. spread.

: If not it seems
: that the bullet retention would be different since the outside of the
: neck was sized instead of the inside. Or do you consider this
: difference too small a factor unless you are benchresting?

I'm convinced that with 30 caliber bullets, it isn't all that important.
Especially since neck tension on most of my loads is so light, I can
easily pull a bullet out of the case with my fingers.  Chronograph
tests show that with a good lot of primers, velocity standard deviation
is in the 5 to 8 fps range; plenty good enough for even long ranges.
Accuracy achieved with such cases is a good as anybody gets.

With .22 and .24 caliber bullets, they tend to shoot more accurately
when necks are turned to more uniform neck wall thickness.  And with
the much closer fit benchrest cases have in the neck area in the
chambers they use, it does help.


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