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Help, concentricity problems.

 
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  #1  
Old 01-20-2007, 10:34 PM
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Help, concentricity problems.

All,

I've been reloading (clean, deprime, prime, powder seat) for 30 years. All my rifles will shoot sub-MOA.

My problem is that until recently, I just worked up a load, reloaded (sorted brass by weight), weighed each charge and called it good.

Since I ordered a 338AM from Kirby, I decided I needed to be able to measure things like bearing surface length on my bullets (so I got some stoney points gauges), Concentricity (so I bought a Sinclair gauge) etc.

Well, I grabbed my box of Norma 7RM brass (mostly once fired, some still virgin, some loaded) and started checking the concentricity.

WHOA!! measured just in front of the neck, the loaded rounds run from .0015 - .008 runout. The once fired measured on the neck runout .002-005" and the new virgin cases run .002-.004" runout.

I immediately measured some of my .243 winchester rounds same type of resolts, then the 7mm-08 same thing, then some factory Remington 7RM, it measured .002-.006" runout

On the .243, I use Pacific neck size dies, on the 7RM I use Forster Neck die, on the 7mm-08 I use RCBS full length.

I polished the expander button on the 7RM Forster neck die, and resized some of the brass; no real change before-after on case neck runout sometimes .001 better sometime .001 worse.

I'm not setup to measure neck thickness.

Since its pretty much the same on 3 different calibers and the factory ammo, do I have a problem? The runout numbers above are extreme spread on the dial indicator. I read that .002" was an allowable limit for runout with bench guns etc. These are all factory chambers with nothing done to the brass but trim/chamfer flash hole debur.

I'm using the same Rock Chucker single stage press I've been using for 30 years.

I now understand the saying "ignorance is bliss".

Any ideas are appreciated.

Thanks,
Don
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  #2  
Old 01-20-2007, 10:58 PM
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Re: Help, concentricity problems.

Don,

Be careful and don't fall into the category of a "tinkerer" as Kirby calls people like me.

If you're getting sub-MOA with what you have and that's been good enough why won't it still be good enough?

I tinkered too much and ruined a bunch of 270AM cases by neck turning just a bit to much. Kirby had said to not turn them, but hey what does he know" [img]/ubbthreads/images/graemlins/crazy.gif[/img]

My run outs, with the sizing die and seating die Kirby sent with the rifle, are 1 thou around the zero mark at best and maybe 3 thou around the center mark at the worst. What I'm trying to say is that the center line of all cartridges is the same. That must be good [img]/ubbthreads/images/graemlins/confused.gif[/img] So I get 2 thou to 3 thou run out.

Having said that, the big girl shoots better than I can shoot it. I'm down to shooting 1 shot groups up to 300 yds and my first and only two shots at 1K were on the same horizontal line and 4" apart.

That was the long answer [img]/ubbthreads/images/graemlins/crazy.gif[/img]

Short answer is Don't sweat it? When you get your AM turning necks will be one of the last things on your list of things to do. And you'll most probably never NEED to get that far down on that list.
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  #3  
Old 01-21-2007, 08:18 AM
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Re: Help, concentricity problems.

AJ

I would have saved you all that money but loaning you my runout device, neck turners, meplaters, and bearing surface measures, The bearing surface measurers are new and never even opened, just looking at them was enough to make me go crawl under the bed and hide. The runout gauge has so much dust on it that you would have to spend an hour cleaning it up.

Your runouts are just minor league numbers compared to mine.

Here is a tip that might or might not help. I do it and like it but my runouts are still 0.01 to 0.007 at the ogive so it did not help me. -- take the spring clip off that holds the shell holder in place and slide a rubber O ring onto the groove. You will have to move it down to put in a shell holder and roll it up again to hold it in place. This will allow the shell holder to move to "line up" as the cartridge case moves up into the die.

Second tip-- as you seat a bullet only pull the handle down far enough to start the bullet and then ease it up and reach in and rotate the case a quarter or third of a turn and then seat the bullet a little more and once more raise the die up and rotate the case still more and then seat the bullet still more. Do this about three times to get the bullet seated. The theory behind it seems to be that sometimes the bullet starts seating misaligned and by rotating you force it into alignment. I do it but I don't really know if it works. I does give you nimble fingers being as your right hand will try to squish your left hand fingers while they are under the die.

The other thing that causes word wars is the Lee Collet Neck Die versus expensive neck dies. I ordered one yesterday because the proponents say they are idiot proof and will give you good neck numbers. We will see.

I am with Roy. If your new gun stays under 0.5 MOA at three hundred yards with just routine reloading techniques then take a box and chuck all of your expensive mental misery devices into it and put them away.

The people who routinely launch bullets past 1K seem to pretty much agree that a lot of stuff begins to matter a lot at those ranges and I guess if a person is going to try for hits past 1K, a person should begin applying every possible techinque to minimize dispersion.
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  #4  
Old 01-21-2007, 08:28 AM
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Re: Help, concentricity problems.

BuffaloBob,

I use that exact technique when seating bullets, don't know if someone told me to do it that way, or I 'thought it up'. Been doing it for years.

Thanks on the shell holder idea.

"Mental Misery devices" LOL, that was great.


Thanks,
Don
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  #5  
Old 01-21-2007, 08:37 AM
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Re: Help, concentricity problems.

I lost that shell holder spring years ago and replaced it with nothing.

I set the shell holder in with the opening facing left which gives the case both the X and Y axis for movement and it stays in place when using it. I have no idea if it helps with run out but sure doesn't seem to hurt and it is convenient [img]/ubbthreads/images/graemlins/wink.gif[/img]
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  #6  
Old 01-21-2007, 08:44 AM
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Join Date: Oct 2005
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Re: Help, concentricity problems.

[ QUOTE ]
Don,

Be careful and don't fall into the category of a "tinkerer" as Kirby calls people like me.

If you're getting sub-MOA with what you have and that's been good enough why won't it still be good enough?

I tinkered too much and ruined a bunch of 270AM cases by neck turning just a bit to much. Kirby had said to not turn them, but hey what does he know" [img]/ubbthreads/images/graemlins/crazy.gif[/img]

My run outs, with the sizing die and seating die Kirby sent with the rifle, are 1 thou around the zero mark at best and maybe 3 thou around the center mark at the worst. What I'm trying to say is that the center line of all cartridges is the same. That must be good [img]/ubbthreads/images/graemlins/confused.gif[/img] So I get 2 thou to 3 thou run out.

Having said that, the big girl shoots better than I can shoot it. I'm down to shooting 1 shot groups up to 300 yds and my first and only two shots at 1K were on the same horizontal line and 4" apart.

That was the long answer [img]/ubbthreads/images/graemlins/crazy.gif[/img]

Short answer is Don't sweat it? When you get your AM turning necks will be one of the last things on your list of things to do. And you'll most probably never NEED to get that far down on that list.

[/ QUOTE ]

Roy,

I'll try not to sweat it, I just don't want something in my control to cause problems with the new rifle. I just want to wring the best I can from it. If I could figure out how to reduce my existing runouts on my existing rifles, then that is cheap education compared to learning those lessons with the new rifle and the expensive components.

Thanks,
Don
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If some is good and more is better, then too much is just right.


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  #7  
Old 01-21-2007, 09:34 AM
Chawlston
 
Posts: n/a
Re: Help, concentricity problems.

Hello,

It is hard to extract all the accuracy from your rifle where the runouts exceed .003" on your loaded rounds. Shooting sub-moa is good for factory rounds (most can be tuned to shoot better), but when you start constructing ammunition yourself, you will find it very easy to get under the .003" runout if you get rid of the expander ball dies and use the bushing style dies along with cleaning up the necks to where the high spots disappear. It is very simple, but you will have to be able to measure the neck thickness or have someone do it for you.

Finally, you can turn the necks to work with your sizing die without the expander ball. I do it on my 30/338 Lapua and it works great.

James
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