How to make rifle cases concentric?

How to make rifle cases concentric?

Post by Clark Magnuso » Fri, 18 Oct 2002 12:40:32



I got a Sincair concentricity gauge.
OK, the accurate ammo seems to be more concentric.
How do I get the brass more concentric?
A die that makes it concentric for a minute will not do it, because it
springs back a few thousands even when annealed.
TIA Clark
 
 
 

How to make rifle cases concentric?

Post by ggline » Fri, 18 Oct 2002 13:25:00



Quote:
> I got a Sincair concentricity gauge.
> OK, the accurate ammo seems to be more concentric.
> How do I get the brass more concentric?
> A die that makes it concentric for a minute will not do it, because it
> springs back a few thousands even when annealed.
> TIA Clark

Clark,

Where on the case are you measuring the concentricity?  Usually, the neck
where the bullet is seated is a source of trouble.  Many reloaders ream the
neck of a case to make the case neck wall of an even thickness all around.
Necks are trimmed for length as well, as the cartridge stretches on firing.
You didn't mention whether you were reloading or measuring factory ammo?

George

 
 
 

How to make rifle cases concentric?

Post by Gunne » Sat, 19 Oct 2002 00:39:07




Quote:



>> I got a Sincair concentricity gauge.
>> OK, the accurate ammo seems to be more concentric.
>> How do I get the brass more concentric?
>> A die that makes it concentric for a minute will not do it, because it
>> springs back a few thousands even when annealed.
>> TIA Clark

>Clark,

>Where on the case are you measuring the concentricity?  Usually, the neck
>where the bullet is seated is a source of trouble.  Many reloaders ream the
>neck of a case to make the case neck wall of an even thickness all around.
>Necks are trimmed for length as well, as the cartridge stretches on firing.
>You didn't mention whether you were reloading or measuring factory ammo?

>George

There are two areas of concentricity that need to be addressed. Case
neck, and bullet. Most bench resters turn the case neck (around a
mandrel), then trim to length.
The most important aspect is bullet seating concentricity. If the bullet
is seated with a slight amount of run out or yawl, it may engage the
lands and groove, and as its swaged down in its passage down the barrel,
it may retain that out of alignment

The line of micro stop Bench rest dies that RCBS puts out, is a unique
idea, that has a sliding sleeve that follows the bullet all the way into
the case mouth. Ive got one for each of my serious cartridges, and axial
rufous is almost dead nut.

Oh..the purists also mark the orientation of the round in the chamber,
and only load it the same way every time. IE..some mark is placed at 12
o clock and each round is loaded with that mark at 12 o clock.
The theory is that the chamber is egg shaped, even a very small amount.
Shrug...

Dont forget to deburr and uniform your flashholes too <G>

Gunner

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How to make rifle cases concentric?

Post by Tom Wai » Sat, 19 Oct 2002 06:36:28



Quote:
>Usually, the neck
> where the bullet is seated is a source of trouble.

Absolutely. The bullet needs axis needs to be perfect with the bore.

Quote:
> Many reloaders ream the
> neck of a case to make the case neck wall of an even thickness all around.

Reaming alone won't improve concentricity, it will only thin the neck wall.
If it started out off center it will finish up that way. Neck
t***/thinning is best done on an arbor that fits closly to the id of the
neck. The cutter is a part of the assembly so the neck wall is uniform.

Quote:
> Necks are trimmed for length as well, as the cartridge >stretches on

firing.

True with overly shortened reloads. Benchrest quality reloads don't strech
much in my experience. The rounds fit the chaamber too close to stretch.
Procedure for uniform cases.
Full lenght size and trim to length.
Ream and deburr flash holes
Thin neck walls to uniform dimension that will give a loaded neck
.001"-.002" clearance in the chamber.
Sort cases by weight or water capacity.
Fire form the rounds in a good chamber.
The chamber must have a tight neck for this to work. Target chambers for 6mm
are typically .262 dia. at the neck. Thus a neck wall of .0105"-.011" will
give you a nice tight one, and we all like tight ones.
A BR quality straight line seating die is a must, it is easily made with the
same reamer that cut your rifle chamber.
Tom

Quote:
> You didn't mention whether you were reloading or measuring factory ammo?

> George

 
 
 

How to make rifle cases concentric?

Post by Clark Magnuso » Wed, 23 Oct 2002 01:44:35


Thanks for the response.

Quote:
>  Many reloaders ream the
> neck of a case to make the case neck wall of an even thickness all around.

I  have a case neck reaming set up that came with the Forster neck
turner.
But I have not bothered to ream any necks, because on the lathe, reamers
always follow the hole.
I use a boring bar when I want concentricity on the lathe.
 
 
 

How to make rifle cases concentric?

Post by Mark » Wed, 23 Oct 2002 02:16:17


Hi all, a while back I tried to clone my very own forster style tool. It
seemed to work ok, but then I got to wondering exactly how far back one
would need to true up the case, I went just short of the shoulder where
it transitions, and upon looking at the cases after resizizing, it was
apparant the cases were s***because of a ridge at the shoulder where I
didnt cut back far enough...    seems like cutting back furthur would
have cut into the sholder possibly making it too thin possibly letting
the bullet take it with it upon firing :-(    Could someone clarify
whats really sposed to happen?
thanks, mark
Quote:

> Thanks for the response.

>> Many reloaders ream the
>>neck of a case to make the case neck wall of an even thickness all around.

> I  have a case neck reaming set up that came with the Forster neck
> turner.
> But I have not bothered to ream any necks, because on the lathe, reamers
> always follow the hole.
> I use a boring bar when I want concentricity on the lathe.

 
 
 

How to make rifle cases concentric?

Post by Gunne » Wed, 23 Oct 2002 03:01:54


Quote:

>Hi all, a while back I tried to clone my very own forster style tool. It
>seemed to work ok, but then I got to wondering exactly how far back one
>would need to true up the case, I went just short of the shoulder where
>it transitions, and upon looking at the cases after resizizing, it was
>apparant the cases were s***because of a ridge at the shoulder where I
>didnt cut back far enough...    seems like cutting back furthur would
>have cut into the sholder possibly making it too thin possibly letting
>the bullet take it with it upon firing :-(    Could someone clarify
>whats really sposed to happen?
>thanks, mark

After first firing, that ridge goes away. In fact, the brass flow will
put that ridge on the Inside of the case mouth.  This factoid is  used
a lot by people who hand seat bullets at the range.

Just turn down to the beginning of the shoulder, no farther. Turn
around a mandrel, and load and fire. Next loading will be with
completly concentric necks.

Gunner

Quote:

>> Thanks for the response.

>>> Many reloaders ream the
>>>neck of a case to make the case neck wall of an even thickness all around.

>> I  have a case neck reaming set up that came with the Forster neck
>> turner.
>> But I have not bothered to ream any necks, because on the lathe, reamers
>> always follow the hole.
>> I use a boring bar when I want concentricity on the lathe.

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How to make rifle cases concentric?

Post by Gary Coffma » Wed, 23 Oct 2002 14:26:57


Quote:


>> Necks are trimmed for length as well, as the cartridge stretches on
>firing.

>True with overly shortened reloads. Benchrest quality reloads don't strech
>much in my experience. The rounds fit the chaamber too close to stretch.

Brass flows under chamber pressure. That's why cases grow in length and
need to be trimmed. With moderate pressure loads, t*** doesn't have
to be done often, but with high pressure loads, it has to be done frequently.

Gary

 
 
 

How to make rifle cases concentric?

Post by Jack Erbe » Sat, 26 Oct 2002 22:35:44




Quote:
>I got a Sincair concentricity gauge.
>OK, the accurate ammo seems to be more concentric.
>How do I get the brass more concentric?
>A die that makes it concentric for a minute will not do it, because it
>springs back a few thousands even when annealed.
>TIA Clark

You want a slight springback for locating and sealing.  Most rifles
are intended to have bolt, chamber, bore, bolt face, etc., parallel,
concentric, or perpendicular as appropriate but manufacturing means
that it will have some deviation.  

One way to compensate for the variance in bolt action rifles is firing
the cases with a rotational positioning reference (the headstamp
markings for example) for the first firing and then only necksize and
fire them in the same orientation.  

You can get several firings with only neck sizing at moderate
pressures in many guns but many factors (neck length, neck thickness,
hardness of the case, etc.) change a little with every sizing and
firing cycle.  

There is no end to the minutiae that some shooters will consider and
attempt to deal with in pursuing accuracy.  They are worse than
machinists.  :>)



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How to make rifle cases concentric?

Post by Jack Erbe » Sat, 26 Oct 2002 22:35:46




Quote:

<snip>
>>..seems like cutting back furthur would
>>have cut into the sholder possibly making it too thin possibly letting
>>the bullet take it with it upon firing :-(    Could someone clarify
>>whats really sposed to happen?
>>thanks, mark

>After first firing, that ridge goes away. In fact...<snip>

Gunner has that right, and your cutter should have some radius at the
point of cut so that it leaves a smooth transition into the uncut
section.  

Make sure you are cutting below the bullet seating depth so that after
the firing puts the ridge on the inside, seating another bullet does
not create a swelled area on the outside of the case.  If that happens
and the swelled area is trapped in the chamber throat as the cartridge
is chambered (the bolt leverage will make this barely noticeable) it
will increase the chamber pressure at firing.   You might get either a
better group, worse group, or a broken rifle.  :>)



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