Setting up a concentricity checker.

Eris

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Jun 16, 2004, 9:17:09 PM6/16/04

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I have no mechanical abilities but there must be an intelligent way to
set up a concentricity guage.

Thanks
Jim

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Clark Magnuson

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Jun 17, 2004, 6:07:33 AM6/17/04

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I have the Sinclair Concentricity checker too.
This picture from the sinclair site shows the neck being checked.
http://www.sinclairintl.com/cgi-bin/category.cgi?category=search&item=09-150&type=store

I don't check the neck directly.
I seat a bullet, position one bearing about as far back as possible
[like the picture], the other bearing about as far forward as possible
without running into the shoulder [as shown in the picture], but I put
the dial indicator stylus on the ogive of the bullet [unlike the picture
that has the stylus on the neck]. That is my standard setup, and when I
write things in my load notes about concentricity, I assume that is the
set up.

After a while, like the instructions say, you will see the .004" of
eccentricity comes from the expander ball. Remove the expander ball,
seat a bullet in new brass that has never seen and expander ball, and
voila, .001" concentricity. That is the end of the first order
problems. Brass that has had an expander ball pulled through the neck is
tricky to rehabilitate to a state of small concentricity. It involves
pushing an even larger expander ball or mandrel through the neck. Some
chambers are big enough [to fix brass by firing] that has had an
expander ball pulled through the neck.

Second order problems: Pay $35 to Forster or twice that to Redding and
get a sliding sleeve seating die, and maybe you will get rid of the last
..001".

Third order problems: Some resizing dies are made with multiple reamers,
and have errors. Forsters do not. Some bullets are not round. Some brass
has variations in thickness around the neck.

Anyway, even with cheap Lee dies, with the expander ball removed, you
can make more concentric ammo than the 75 cents a shot Federal Gold
Match ammo or Black Hills or what have you..
Then you won't need the concentricity checker any more, once you learn
what it has to teach you.

Eris wrote:

> ...

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A society that teaches evolution as fact will breed a generation of atheists that will destroy the society. It is Darwinian.

Bart B.

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Jun 17, 2004, 9:19:34 PM6/17/04

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If you mean getting a gage that's already made set up, follow the
instructions packaged with it.

Otherwise, it depends on what kind you have.

I've used one or another over the years and I prefer my home made one.
Two M1 military cleaning rod sections (1/4th in. dia. but could use
any rod of same size) screwed and nutted about 3/4ths inch apart
between two aluminum blocks on each end. Two ball bearings that's a
slip fit on the rods and half inch in diameter is where the bullet
rests just in front of the case mouth. Two more bearings set so the
case's pressure ring rides on them. I put the dial indicator vertical
directly over the bullet and two calibers (bullet diameters) in front
of the case mouth. The gage then works like a roundness gage (V-block
with vertical dial plunger above it) and is the best way to measure
anything for roundness.

If I slide the front bearings back onto the shoulder-body junction, I
can measure case neck runout.

Ken Marsh

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Jun 19, 2004, 9:08:16 AM6/19/04

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Hi,

Clark Magnuson <c.mag...@comcast.net> wrote:

#Anyway, even with cheap Lee dies, with the expander ball removed, you
#can make more concentric ammo than the 75 cents a shot Federal Gold
#Match ammo or Black Hills or what have you..
#Then you won't need the concentricity checker any more, once you learn
#what it has to teach you.

Welllll..... I find that an occasional case comes out bent no matter how
careful you are. I suspect that it is the result of uneven case lube
distribution in some cases, or just factory uneven brass thickness
waiting to show its ugly head. In any case, if you want to shoot really
tiny groups without any flyers, I would recommend checking all your
reloads.

Ken.
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Clark Magnuson

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Jun 19, 2004, 4:41:08 PM6/19/04

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Welllll..... perhaps I exaggerated.
I still have mine and use it occasionally.

--
A society that teaches evolution as fact will breed a generation of atheists that will destroy the society. It is Darwinian.