Case stretch

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by nddodd, Aug 7, 2010.

  1. nddodd

    nddodd Well-Known Member

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    What is a normal amount of case stretch in a rifle that is headspaced correctly. Mine is stretching .005 just wandering if this is good or bad.


    Thanks fellas,

    Nathan
     
  2. Mikecr

    Mikecr Well-Known Member

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    With a stiff load, or mid to long/skinny case, narrow shoulder angle, & FL sizing, I would think it's somewhat common. I have a friend that trims his 25-06 very regularly.

    In contrast, none of my cases lengthen at all. My situation is just opposite above.
     

  3. J E Custom

    J E Custom Well-Known Member

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    You may be over sizing . After firing size just enough to be able to chamber. And then check
    the growth of one of these rounds after fireing. If it still grows that much you may have to back
    off on the powder charge.

    If a round is sized properly and fired in a good chamber it should not grow very much unless
    it is a hot load and then the chamber can grow enough that the brass will expand and
    spring back will after firing and ejecting will be larger than the chamber.(This is the case when
    you have heavy bolt lift.

    J E CUSTOM
     
  4. nddodd

    nddodd Well-Known Member

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    I guess I shouldve explained it in different way, Im wandering if I have excessive headspacing or not. Using nosler brass in .243 win unfired then firing and measuring the shoulder of the 2 there is .005 diff. Of course the fired being longer. Just curious if .005 is normal or should it be less if headspaced correctly.

    Thanks,
    Nathan
     
  5. SBruce

    SBruce Well-Known Member

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    I would think that .005" is very normal for a once fired case. I've seen that much expansion/stretch in alot of factory guns.

    I am getting some custom dies built for a new wildcat. The die maker requires cases that have been fired 3 times to make the perfect die. This tells me that new, unfired cases are usually alot smaller than a chamber is. I believe the allowed varience in factory chambers (SAAMI specs) is .010" between go and no go. Therefore, new brass would have to be small enough to chamber in the SAAMI Minimum chambers.

    I highly suggest an RCBS Precision Mic. It is a multiple use tool that will measure your headspace (off of a fired case), aid in setting up your FL die so it just barely bumps the shoulder, it will measure the Boltface to Lands in your gun, and also provide you with a tool to measure the cartidge Base to Ogive of a loaded round (so you can adjust the seating die for maximum accuracy)

    I've been using them for many years in factory chambered guns. For the simple fact that some factory chambers are on the excessive side.
     
  6. justgoto

    justgoto Well-Known Member

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    You need to use HEADSPACE GAGES (GAUGES) to find out..
     
  7. shortgrass

    shortgrass Well-Known Member

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    The difference between GO & NO-GO in the .30/06 (and its cousins) is .006" For the .308 Win. (and its cousins) it is .004". The Weatherby Mags. is .003". The only way to check headspace is with fixed, tool steel gauges.
     
  8. SBruce

    SBruce Well-Known Member

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    Thanks for the correction, I didn't realize it was that small.

    I still recommend the Precision Mic, because you can use it to set up your reloading dies for whatever headspace you have......excessive or not.
     
  9. shortgrass

    shortgrass Well-Known Member

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    Hey,,, I'm just full of little tidbits of obscure info. That .006" tolerance must be the limitation the brass as it is still the limiting component for the pressures that are generated as the propellant burns. The higher the pressure the tighter the working tolerance. We count on the brass case to stretch and then contract some, so it can be extracted from the chamber. By design and by the nature of brass. I would suspect case stretching, like the OP asked about, comes from high pressure cartridges or 'generous' chambers or both. .005" 'growth' wouldn't bother me too much, but, when I resized those cases I'd only re-size enough to ensure reliable function in my rifle. That will help limit 'growth' and/or hard brass for future reloadings.
     
  10. nddodd

    nddodd Well-Known Member

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    Thanks guys that's what I was wanting to hear, I'll tell you what I did to headspace. It's a savage PTA that I ordered a shillen barrel for. I used a new unfired piece of nosler brass screwed the barrel in until I could no longer work the bolt backed out a hair tried again so on and so forth until I could close the bolt with out any resistence. Does this sound ok or should I have ordered a no-go gauge.

    Thanks,
    Nathan
     
  11. shortgrass

    shortgrass Well-Known Member

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    Headspace gauges are the only accurate way to set headspace. By using unfired brass your chamber/bolt face relationship is, no doubt, short. The 'tight chamber, neck turned, bullet touching the lands stuff is all bench rest type stuff where each round is single loaded, not fed from a magazine, and then used at a shooting bench. I want my hunting rifles to be accurate but not at the sacrifice of reliability. Get some gauges or visit your local gunsmith and set that new barrel to specs.
     
  12. Fitch

    Fitch Well-Known Member

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    That question, "Is the rifle properly head spaced?", is answered with Go/No-Go gages, not brass. Brass is about as dimensionally stable as soft cheese compared to precision ground Go/No-Go gages.

    That said, 0.005" from factory new brass to once fired brass is relatively common. How much it stretches on the second firing depends on how you size the brass, not the rifle chamber. If you size it to "just" bump the shoulders .002" or so, it will chamber and won't stretch nearly as much. If you neck size it it may be a trifle stiff to chamber but it won't stretch much, if at all.
     
  13. nddodd

    nddodd Well-Known Member

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    Thanks for the reply fitch that's exacly what I'm doing fl sizing and bumping the shoulder back .002 tried neck sizing but after the second firing the bolt was a little stiff. I'm getting better accuracy by bumping the shoulder anyway.

    Thanks again,
    Nathan