cases streatching - headspace?

Discussion in 'Reloading' started by RustyRick, Aug 15, 2013.

  1. RustyRick

    RustyRick Well-Known Member

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    I trimmed all my cases to the correct length and then loaded for testing loads. 3 powders, 3 shots per load, and 6 groups not as high as the book maximum.

    90 % of the cases including my lowest loads will have to be trimmed again.

    I have never see this before. It's my brothers gun which hasn't been preforming satisfactorily. No groups responded as I would expect so I quit with 15 of the 54 cartridges un-shoot.

    I was suspecting a action to wood stock issue so I took out the clip and will try again tomorrow.

    But the case stretch - could that be a head space problem?
     
  2. jimbires

    jimbires Well-Known Member

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    if this is new brass it can be made fairly small to be sure it will fit any chamber .

    if it is used brass I'd say you are over sizing it . you need to have a way to measure a fired case then adjust your die so you are only pushing the shoulder back about .002 . even if the chamber is cut on the large side you can adjust your die to properly size the brass .

    I use a RCBS precision mic for measuring my fired case . I use the redding competition shell holder set to be able to easily adjust my sizing die . Jim
     

  3. g0rd0

    g0rd0 Well-Known Member

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    good advice about the setting of the dies.
    Give that a try but, if that dosn't work contact forster and get a nogo gauge. The nogo is simple to use just drop it in the action and close the bolt, if the bolt closes then your head space is out to lunch and needs to be turned back.
     
  4. jsthntn247

    jsthntn247 Well-Known Member

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    I'm having the same problem with mine with the exception that mine is shooting 1/4" groups. It's a target rifle that I trim brass to 2.007 and after firing the brass measures 2.017. I use a body die each firing and only bump shoulders .001 measured on a headspace gauge. I can't figure out why I'm having to size so much either because the load shows 0 pressure signs and is 1.5gr under max. Interested in seeing replies.
     
  5. boomtube

    boomtube Well-Known Member

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    I can. Shoulder length is only part of the issue, it's probable your chamber is quite a bit larger in diameter than your size die so the body gets squeezed during sizing and that metal does go forward. That's when neck sizing is actually worth something.

    Within reason, headspace should be meaningless to a competent handloader; make cases to fit the chamber and the ammo will be perfect.
     
  6. Bart B

    Bart B Well-Known Member

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    Every rimless or belted bottleneck case I've fired is a few thousandths shorter (head to mouth, or case length) after firing. Fired case shoulders are set back 1 to 2 thousandths each time.

    Every one got longer when full length resized.

    Each case's shoot size, reload cycle grew the case about .001". So they were trimmed back to my spec every ten cycles.

    I think everyone elses cases do the same thing. But measure the case length before it's reloaded, after it's fired then again after it's full length sized.
     
  7. jsthntn247

    jsthntn247 Well-Known Member

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    Just body sized the brass and bumped shoulders .0015. The case grew .003 in length.
     
  8. RustyRick

    RustyRick Well-Known Member

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    My SAAMI length is 55.12. I measure and trim cases after resizing. And I hade many cases upwards of > 55.4

    That seems a lot in my mind.
     
  9. Mikecr

    Mikecr Well-Known Member

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    You guys are squeezing the brass up like toothpaste, and trimming it away to change your case capacities, and create donuts and runout.
    The results of choices you make..
     
  10. Bart B

    Bart B Well-Known Member

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    Mike, while this might be one of your favorite axes to grind, for the benefit of all the others who do, here's some realities regarding it.

    Many top ranked rifle shooters winning matches and setting records have been doing this very same thing for decades. When done in moderation, the benefits far out weigh an insignificant change in case capacity (after 5 cycles, it may require a 1/18th MOA correction on the sight) but it's never been a concern as far as runout becoming an issue. Such practices have produced test groups in their rifles smaller than current benchrest records.

    The folks who do it the most are those few who full length resize fired cases testing match bullets for accuracy at Sierra Bullets' plant in Missouri. The best of those HPMK pills shoot into 1/4 MOA in their 200-yard test range.

    While you may regurgitate from mental nausea at the thought of doing what other successful folks have done, that's fine by all of us who do. Take a deep breath, relax and be sure you've enough paper towels and tissues to clean up the mess you make.

    Exactly how much case capacity is changed by removing a cartridge brass tube .335" diameter, .010" long with a .013" wall thickness thats removed form a 30 caliber cartridge case that weighs 200 grains? How much of a change in point of impact will that make?
     
  11. Mikecr

    Mikecr Well-Known Member

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    Other than point blank BR I suppose, not all competitive/record holding BR shooters FL size.
    At least not in LR BR. Not all anneal every reloading either. That notion out there is just completely fabricated. Truly there is nothing that ALL do.
    The way I see it, the basis that 'everyone is doing it' is not born of reasoning, and therefore unlikely to change as a result of reasoning.

    For those who are content with their FL sizing, I'm glad for them. I know there are situations where FL sizing is appropriate, and I'm not out to convert them.
    But many many issues, directly resulting from FL sizing and continually puked across shooting forums, are merely the result of choices.
    This is where I go with it. To inform folks that they are not locked into these issues, despite advice elsewhere. They can plan, make choices, and stop chasing their tails.

    You and I don't agree, and you have your messages and I mine. It makes for good contrast in discussion and I don't wish to ruin threads with personal attacks. Let's not.
     
  12. boomtube

    boomtube Well-Known Member

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    You set the shoulder back .0015" from fired position? You know that fired position is at least a thou less than the chamber length? The firing pin will drive most bottle neck cases forward another thou and then the exploding primer will do almost that much more? End result would then be close to 1.5 + 1 + 1 = 3.5 thou shoulder set back with ignition which will require almost that much stretching when fired again. If you're gonna shoulder bump every time you will likely get pretty much that result every time. :D
     
  13. jsthntn247

    jsthntn247 Well-Known Member

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    What is your suggestion. I'm not here to get in a piszing match, I'm trying to learn.
     
  14. Bart B

    Bart B Well-Known Member

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    I agree the firing pin drives the case forward until its shoulder stops against the chamber headspace point; chamber shoulder for rimless cases, rim or belt shoulder in the chamber for these.

    I've fired dozens of live and dead primed empty rifle cases as well as near two dozen live and a dozen or more dead primed and bulleted rifle cases without powder in them. None of them had any evidence of the primer alone drive those bottleneck cases forward. Shoulder setback was the same across all of them. Those with bullets seated did not move the bullet at all from the live primer firing. And all the primers remained flush with the case head as they were when first primed.