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Concentricity:How much ?

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Unread 02-15-2010, 04:53 PM
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Join Date: Feb 2008
Location: Sonoma County, CA
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Re: Concentricity:How much ?

Iíll have to say, as much as I really enjoy reloading, I have been trying to avoid neck turning as long as possible. As I mentioned earlier, I have sorted my brass by neck wall variation and I believe it has worked well for me up to this point. I have always tried to maintain two piles, one that was .001 or less and the other that was .001 to .002. To be honest, I donít know if these two piles shot any different or not. Also, TIR pretty well matched the variation measurements.

JE, as you know, lately Iíve been having some major runout issues with Rem 300 Ultra brass. I did a test a while back with 9 rounds, measuring the brass during every step of the process. I sorted new cases by neck wall variation. I couldnít be too picky with this but ended up with the best three having neck wall variations of .0015, .0015, and .0025. The runout at the neck was .0015, .002, and .0025. Neck wall variation pretty much stayed constant with runout. Loaded round TIR as measured at the ogive was .0015, .002, and .0025. Again, fairly constant at this point. At the bench, these three rounds shot a center to center of 0.25 at 100 yds.

Now, some of the other cases started out with neck wall variations of .0035, .0035, and .003. TIR at the neck was the same. TIR at the ogive was .007, .006, and .006. It was almost like a trickle effect. They started bad and just got worse, doubling when measured at the ogive. I guess this may be due to the measurement being taken farther down the case in that it becomes more apparent. These shot fairly well with a measured group of 0.4. I was a little surprised they did as well as they did, but the group size did increase, almost doubled.

Finally, the worst cases of the bunch were neck variation of .0045, .0045, and .005. TIR at the neck was .0045, .0045, and .005. Again, the same. TIR at the ogive was .0065, .0075, and .009. These three shots were loaded the same, just had terrible runout numbers and the group opened up to 1Ē+.
Unfortunately I am unable to find decent brass in this caliber, atleast for the time being. I have a feeling that neck trimming would be beneficial to the overall accuracy potential of this brass.

TnTom, ď If the necks are pliable, clean and the walls are relatively uniformĒ. That sounds like solid advice. I have noticed in other calibers when the brass starts to get a little hard around the necks. I havenít tried annealing yet but have been reading up on it as well.

During this test, I weighed all of the brass and could not find any correlation between this. Also, naturally this is not a scientific test under a controlled environment, just one guy messing around at the bench. Hope it helps.
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Unread 02-15-2010, 05:03 PM
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Join Date: Apr 2005
Location: Alaska
Posts: 4,895
Re: Concentricity:How much ?

Outside neck turning isn't that difficult or expensive. Takes a little time but done properly - the first time is the last time it's necessary. I use a K&M Services neck turning tool with a battery powered drill to outside neck turn. Works well. There are some tricks to ensure you don't develop the dreaded doughnut after outside neck turning, and to ensure the first turning is the last you'll have to mess with it any further. 6mmbenchrest site had a good article on it as I recall. Or Google and search for more detailed information.

Based on the limited measurements you've collected so far, it would appear that outside neck turning will improve your consistency and accuracy with the 300 RUM brass.
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Unread 02-15-2010, 06:17 PM
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Join Date: Dec 2009
Location: middle tn
Posts: 72
Re: Concentricity:How much ?

like Phorwath said nothing complicated about it. Take some old brass and and exoeriment with it then you'll feel in control when you do your good stuff. No biggie.

I did have a Lyman that was defective from the factory and couldn't get a decent concentric neck. The mandral was eccentric to the bit and no way would it ever make a good case but when I discovered what was going on and replaced it the process was a piece of cake.

when you try it just concentrate on removing as little material as possible to save getting the wall too thin. No need to.

Annealling is also something some folks discourage as if not done correctly it can lead to problems to do your homework and its another process that can make a difference and a process you can do with confidence. There are some do's and don;t involved.
don't ever be fooled into believing security is a good alternative for freedom.
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Unread 04-08-2010, 09:05 PM
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Join Date: Nov 2009
Location: Timber Lake, South Dakota
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Re: Concentricity:How much ?

Originally Posted by Moman View Post
+1 on this technique. I FL size with custom honed Forster FL Comp dies with an expander. After sizing, I measure runout at the case mouth along with neck wall variance and make sure they match. As long as they match, I figure any runout shown will be due to neck wall variance and the centers should be true. I don't neck turn so this is the best I can do at this stage. I sort brass by neck wall variance and only keep .001 or better for long range work. This has helped with much better TIR and long range accuracy.

As far as the magic number, I am striving for 0 runout but usually end up with .001. Lately I've had some problems with runout that I associate with poor brass and a tweaked press. This has absolutely killed accuracy. Some loads jumped up to .006-.011 and accuracy opened way up in the 1" range. A little embarrasing that this snuck by me, but life is life and corrections are being made.

As 300RUM mentioned, paying attention to all details is critical.
Impressed that someone is this honest! I'm interested as I just bought the Hornady and I'm wondering if it's any good.
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