Do I need to neck turn?

Discussion in 'Reloading' started by ZSteinle, Mar 18, 2013.

  1. ZSteinle

    ZSteinle Well-Known Member

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    7mmSAUM, shooting necked down norma 300 SAUM brass
    Reamer neck diameter 0.321
    Loaded case neck diameter 0.316
    Full lenght sized unloaded case 0.314
    Fired case diameter 0.319
    redding standard fell length sizer was the die I used

    Reason I ask is I loaded up some ammo off of Berger reloading manual. used their 168 VLD to start with but was shooting 162 hornday match bullets so I figured it would be fine but was showing some pretty good amounts of pressure. fired 2 rounds and stopped there.

    Load was 56 gr. of 4831sc at 3.060" OAL
     
  2. Lefty7mmstw

    Lefty7mmstw Well-Known Member

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    Hodgdon shows your charge as start charge for the hornady 162 in the 7 saum. Are you on the lands or are you giving it a bit of a run??
    5 thou clearance should be fine. You aren't that tight as the fired diameter is also a few thou. above loaded diameter.
     

  3. ZSteinle

    ZSteinle Well-Known Member

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    They are about 10 thou off the lands. Another thing i am used to is with a fired case i have been told a bullet of the same cal should slide in easily. I think I could literally punch out the primer put in a new primer add powder and seat a bullet.
     
  4. Lefty7mmstw

    Lefty7mmstw Well-Known Member

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    If you are tight enough that you can't put another pill in of the same cal. you may want to turn a bit. It seemed from your measurements you had a bit of breathing room. Think about backing the bullet up a bit too at least to start with. Giving it a bit of run will ease pressure some.
     
  5. ZSteinle

    ZSteinle Well-Known Member

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    Just tried again to put a bullet back in the case and I can seat a bullet with some force and pull it back out by hand. Seems like trimming of 0.001 would help but dont really want to do it unless necessary. I will start with a lower load and start to work up and see what it does first.
     
  6. Bart B

    Bart B Well-Known Member

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    Bullets should be held tight enough to not easily be pulled out by hand. It doesn't matter accuracy wise how much clearance there is between the case neck and chamber neck. The neck centers perfectly in the chamber when it's fired anyway, regardless of the clearance amount.
     
  7. Lefty7mmstw

    Lefty7mmstw Well-Known Member

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    Bart, he's talking about fired rounds not accepting another bullet easily(on a fired brass without re-sizing); ie. he's not getting a good release.

    What is your brass's trim LENGTH in relation to your chamber dimension?? I'm starting to wonder if you aren't at the end of the chamber and dang near crimping the brass into the pill when you chamber.

    "Loaded case neck diameter 0.316
    Full lenght sized unloaded case 0.314
    Fired case diameter 0.319"

    From your loaded diameter to your fired diameter there's .003" expansion; that should be sufficient.
     
  8. Bart B

    Bart B Well-Known Member

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    Lefty, thanks, I just realized that myself.

    It doesn't matter if the case is several thousandths shorter than chamber length. A couple thousandths shorter necks has no noticable effect on anything.
     
  9. boomtube

    boomtube Well-Known Member

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    I've made a couple dozen chamber casts to measure the necks. As a general rule I've found the chamber neck will be about a thou larger than the diameter of a fire case.
     
  10. ZSteinle

    ZSteinle Well-Known Member

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    took the rifle out again today. Loaded up 180 grain bergers about 20 thou off the lands starting load was 51gr. of h4831sc. Loaded up 6 rounds starting at 51 and going up in 1 grain incriments. all the fired rounds and easy bolt lift, no signs of the pressure there, the primer looked good but there were some slight ejector marks on the cases. I didnt crono them but I wish i would have being that the 53gr load 54grain load 55gr load and 56gr load all ended up shooting into a group that measured 0.330" outside to outside. I will post up some pictures when i get a chance
     
  11. ZSteinle

    ZSteinle Well-Known Member

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    [​IMG]
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  12. AZShooter

    AZShooter Well-Known Member

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    Great package! You have enough clearance based on the dimensions you posted.

    My friend Dan, a 1000 BR shooter, runs a 7 SAUM for his light gun. He is also necking down the 300 SAUM. He uses .001" clearance per side BUT he turns the necks. He also turns them every time before reloading them. With such a small amount of release he has no room for error. His rifle won best agg, tightest group and high score first time out! He shoots the 180 hybrid target.

    You are running .0025" per side IF every piece of brass has the same neck thickness. There is some springback after firing. I also have a snug neck with my 7mm/375 Ruger after firing and cannot push a bullet down the neck by hand and it is running .003" clearance per side . FYI all cases were turned to .0135" to fit a .317 neck.

    Did you measure every loaded round? Perhaps a few got by you that were thicker. It won't hurt performance to skim turn all cases to ensure the neck wall thicknesses are the same. I would bet there are a few that are thicker. This would also help with consistent neck release.

    Perhaps there is more bearing surface on the 162 hornady match bullet than the 168 VLD causing your load to appear to be too hot. There could be other factors in your particular rifle and the reason we have to start low and observe how the individual rifle responds.

    Be sure to share anything you learn as you continue to work with your new rifle.
     
  13. Bart B

    Bart B Well-Known Member

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    I don't think it matters how much clearance there is between a rimless bottleneck case neck and the chamber neck as long as the case neck's well centered on the case shoulder. Those with .005" clearance all the way around will center in the chamber neck just as perfect and repeatable as those with .001". Chamber and case body and neck diameters do not determine how well centered such cartridges align themselves in the chamber.

    More important is how well centered the case neck is on the case shoulder. That's what determines how well centered the case neck is in the chamber neck. And a half thousandths spread in neck wall thickness doesn't seem to matter. Having shot sub 1/2 MOA 15-shot test groups with virgin brass with near .001" spread in wall thickness at 800 yards and further, I'm convinced there's other stuff more important to good accuracy.

    If one has the tools to do so, measure the force needed to pull bullets across a batch of seated bullets in cases with different amounts of neck wall thickness. Most folks who have done this are quite surprised.
     
  14. TracySes23

    TracySes23 Well-Known Member

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    This question may be a little bit off the subject, but what would be the minimum neck wall thickness acceptable & still be safe?