Case neck runout

Discussion in 'Reloading' started by Firearrow, Nov 14, 2013.

  1. Firearrow

    Firearrow Well-Known Member

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    I just start check case neck runout and measuring neck thickness. So I had a few questions. If it makes a difference I am working with new RWS brass that has been ran through a neck sizer and will be for a 300 win mag.

    First, what is acceptable runout on the case neck, and is this number also good for when you check the runout on the bullet? I have some that are .001 and some that are .006. With the cases that have more runout, I measured the wall thickness and there was a difference in thickness. This means that the cases that have a larger difference in wall thickness need to be neck turn???????

    Second, what is the correct way to determine how much material to remove from the neck when you are neckturning. Once again not sure if this means anything but my rifle does not have a factory barrel. So, am I looking for a consistent thickness in my brass from the thinnest measurement off of the case wall at the neck. Or, am I looking for a consistent thickness in my brass that is just a touch smaller than neck in the chamber?

    Third question. Does the brass need to be fire formed before any of these measurements means anything, or is vergin brass the best to start with?

    I really hope what I wrote makes since, and thanks for the help.
     
  2. woods

    woods Well-Known Member

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    Here's my opinion. It may not be the best but it's the advice I follow :D

    Outside neck turn to the thinnest thickness on new brass. IMO a consistent neck thickness is more important than minimizing neck clearance in the chamber.
     
  3. yoterunner

    yoterunner Member

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    Woods,
    In your opinion what is most important, run-out or neck tension for consistency thus accuracy? I'm trying to learn about both and see what I can do in my reloading process to make improvements. I do want to go one step at a time to see the affects of any change.
     
  4. Derek M.

    Derek M. Well-Known Member

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    The more proper brass prep done, the better the accuracy results should be. That's my advice.
     
  5. woods

    woods Well-Known Member

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    Wow that's a hard one.

    It would depend upon a couple of things

    I chased runout many years ago first and solved it with the Lee Collet neck sizer so don't worry or even monitor it anymore

    I do pay particular attention to neck tension and do monitor it with pin gauges. The Lee Collet with special order mandrels also gives me the exact neck tension I want.

    Consistent bullet release is critical to a consistent seating depth and velocity, so I would say

    Neck tension (IMO)
     
  6. yoterunner

    yoterunner Member

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    Yeah, I have been thinking about the Lee CNS die. I shoot 300 RUM, so will have to special order it. I use Nosler brass, but have not kept track of # of firings between the brass, so I think my neck tension is varying a bit. Am I correct that I should anneal all the brass and start over with even neck tension using the CNS die?
     
  7. woods

    woods Well-Known Member

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    If you do order a die from Lee, order some undersize mandrels at the same time. They are cheap but there is a minimum order dollar wise. The die should put you over the minimum.

    I would order a mandrel at .306" & .305". Then you can experiment with a better bullet grip than the mandrel which comes with the die will give you. It should be about .307"

    Your actual bullet grip will vary a very little bit because of the work hardening or annealing practices. Work hardened brass will springback more and eventually you will get less bullet grip. Annealing at that point will give you more grip.

    With the 300RUM I would recommend (again my advice is worth what you are paying for it) trying for a grip of at least .002" and .003" is usually what I like.

    There is a learning curve with the LCNS and different opinions on adjustment but adjusting according to directions is always a good place to start.

    Your runout on the case neck will not be absent if you have a big variance in your neck thickness, but the runout on the bullet should be good. IOW the LCNS will make the neck ID consistent and push the neck thickness variances to the outside of the neck.