Chambered Round Alignment to Bore; Neck Sized vs Full Length Sized

Discussion in 'Reloading' started by Bart B, Apr 25, 2012.

  1. Bart B

    Bart B Well-Known Member

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    Another curiosity poll...........

    With rimless bottleneck fired cases, neck only versus full length sized, what's the difference in how they fit the chamber and align the bullet with the bore when the primer goes off and fires the round?
     
  2. Mikecr

    Mikecr Well-Known Member

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    Well the least sized of fireformed brass will certainly 'fit the chamber' with higher precision.

    Nobody walking this planet knows for sure.

    As far as anecdotal evidence, IMO, there is none credible.
    Both perfect fitting and sloppy have performed well enough amidst the abstracts of trial & error in the shooting community. And I've seen no comprehensive testing to implicate valid conclusions here.
    That is, nobody who can has proved that perfect fitting is better or worse than sloppy fitting.

    Also, there are still reloading pros and cons to every action/approach.
    just part of the abstracts, and of many things left for us to learn..
     

  3. rscott5028

    rscott5028 Well-Known Member

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    Neck sized brass more closely fits the chamber dimensions when used in the same good, concentric chamber it was last fired in.

    I have no way to measure how well either one centers and don't really care except as a curiosity.

    I've yet to see proof posistive that one method consistently outperforms the other for precision shooting.

    Either method done right will outperform us humans. And, that' increasingly true the farther you shoot.

    JMHO
    -- richard
     
  4. reelamin

    reelamin Well-Known Member

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    Go to any BR match for any "Proof Positive" you may need that neck sized/fired cases are more accurate and centered to the bore. Show me one of them that is shooting FL sized cases. The physics apply to any rifle.
     
  5. BountyHunter

    BountyHunter Writers Guild

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    BIG MYTH.

    Go and you will find that in fact in LR most are FL sizing and polls on BR central showed most are FL sizing in SR also. Harrel brothers make one of the best FL dies for the PPC and different ones to fit most of the chambers.

    Two of the very best SR shooters around (Tony Boyer and Mike Ratigan) have both in the last two years published very detailed books about how to do it. They both have very strong opinions that FL sizing is the way to go and is required unless you are shooting extremely light loads, which almost no one does.

    We have even had one of our "NS only" gurus go there and try to educate the unlearned masses with no success as expected.

    I will say that in the LR game, more than one top shooter has found out that the best concentricity and uniform neck tension is coming from a hybrid technique. They FL size first, use neck expanders (K&M or Sinclair) to expand the complete neck back to nominal caliber and then use a NS only die to neck down to the desired dimension.

    For several years it was a very quiet technique but recently has become known more widely.
     
  6. barnesuser28

    barnesuser28 Well-Known Member

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    the Hoover family uses this technique and they are VERY successful in the 1000 yard BR game. here is a link to accurateshooter.com 6.5-284s of the Hoover Clan within AccurateShooter.com
     
  7. rscott5028

    rscott5028 Well-Known Member

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    Assuming you are referring to group size, and further assuming that BR shooters are the most precise shooters of all, I'm still not willing to stipulate that smaller groups imply one method is more centered in the chamber. How did your BR friends measure centering in the chamber?

    Likewise, the popularity of one vs the other for any given shooting discipline isn't proof positive of centering or group size.

    There are many pros and cons to both methods.

    Nonetheless, it was a seasoned benchrest shooter that got me to change over to FL sizing for my 6br. So, I'm not even certain that your ascertion that most BR shooters prefer to neck size is necessarily correct.

    I do however agree that "physics apply to any rifle." I would add that physics applies to bullets as well. I'm just not sure what it has to do with centering in the chamber.

    Then again, I'm not sure exactly how much runout it takes to reduce accuracy; nor what that little ejector plunger off to the side of the boltface does to help center a round precisely; nor if we're talking about once fired/neck sized vs 5 times fired/neck sized and almost unable to close the bolt. Is the case and/or the bullet getting more centered each firing? Do your groups just keep getting tighter? When you finally decide to bump your shoulder, does your precision shooting suddenly fall apart?

    -- richard
     
  8. Mikecr

    Mikecr Well-Known Member

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    What the Hoover family does to be successful, is more likely a combination of many things unrelated to this subject. Right?
    And even if you were to discard all the actions a competitor takes to actually represent competition, to imply it comes down to mere sizing technique, there still remains no credible evidence of it.
    After all, maybe the Hoovers can and will do better still.
    Maybe they do well despite their sizing techniques.
    Maybe you don't even know what they do, and how they do it, and with what & why.

    It's kind of silly to create a NS-ONLY -vs- FL sizing contest, for a question there currently is no answer to.
    Hell, if it were really a contest, then both could very well lose.

    Now, if someone proved, through some chambered laser technique, etc, that one point in case sizing provides better bullet alignment with a qualified bore centerline, for a given cartridge and chamber reamer, and chambering method, then there could be discussion about the contributors and results in this.
    And with this, the pros and cons to it(a contest in a sense).

    I am interested enough to do such a test, but I haven't the time & resources now.
    Maybe someday...
     
  9. BountyHunter

    BountyHunter Writers Guild

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    No one can measure "one" thing to say this is the most important thing. It is a combination of the parts.

    The point/inference about the alignment being the key is misleading IMO for several reasons.

    Cases do not suspend in air inside the chamber. They are held front and at the rear by the bolt and extractor regardless of what sizing method. Very few people realize and talk about the part the bolt plays in centering the round.

    The issue of case sizing has more to do with uniformity of the case, reliability of loading and extraction, and reliable neck tension which will open/close groups. We can argue the FL vs NS repeatedly and will I am sure for accuracy, but to me it is reliability of case in and out of the chamber without being tight or hard extraction and uniform case dimensions.

    Again, there is a growing awareness that super tight necks in the LR community are not necessary. It used to be you had to have no more than .015 total clearance and now many top shooters are going with as much as .03-.04 total clearance as long as the body is uniform, the necks are annealed and you have a uniform tension (which is the hardest to control).

    BTW I knew John Hoover what John was doing with the neck tension 4-5 yrs before the article. As I said, it was being used by some before being written up for all. By using a NS die for the final step, it always leaves a little ridge to help center the case except for the Neil Jones and Warner dies which are different and go all the way down on the shoulders.
     
  10. Deerndingo

    Deerndingo Member

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    There are too many variables to make a call between FL and NS. What I do know is that I get just the same accuracy with a FL round and I do with a NS round. Though I do use a K&M neck expander once I have FL sized. Interestingly, I can get more FPS out of a FL round, but that's another story.
     
  11. Mikecr

    Mikecr Well-Known Member

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    You get more velocity from a FL sized case, for a given load, because it's smaller as sized, increasing load density.

    As far as shooter trends;
    IMO taking under capacity/purpose built cartridges to extreme pressures has allowed competitors to work around the pitfalls of taking shortcuts(like accepting huge neck clearances). And with this, shooter results aren't really progressing beyond past accomplishments. They are good enough, with less efforts, and I don't give credit to this beyond appropriate.

    A coworker doesn't bother with bullet seating tests, or precisions in case preps, sizing, powder weighing, etc. His 30br can whip pretty much any hunting cartridge for accuracy within 300yds, and for no more effort than producing the highest peak pressure he can.
    Sadly though, it fosters notions that nothing else pays off as much, so 'why bother'..
     
  12. Trickymissfit

    Trickymissfit Well-Known Member

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    * what happens when you pull the trigger?
    The primer goes off and starts the powder burn, and then causes a gas build up inside the case. Similar to a pneumatic gas cylinder. Everything expands in every directions till it meets enough resistence that it can't move anyfurther. Pressure then pushes the bullet thru the barrel. When the gas pressure reaches a certain point the brass case starts to expand, and then when the pressure is decreased to a certain point the case retracts back towards it orginal deminsion. That's called spring back, and they all do it.

    * Now we have twelve cases. Six are run thru Joe's space age full length die of somekind or another. Cases are sized back about .003" all the way around. But the other six cases are left untouched demensionally with the exception of shrinking the neck diameter. One set of cases has about .0045" of clearence in the chamber berses the case body. The other has about .002" clearence. The latter will have better alignment because of the amount the full length die resized the case. Yet neither one is perfect, but one of the is less than the other. Of course there's also the issue with the datum line in the shoulder verses the chamber giving a tighter lockup in the chamber (I'll let all of you cuss and discuss this)

    ** BUT! What if you built a full length die that sized the case exactly .0015" all the way around with a bushing that sized the neck about 75% of the length? The bushing would float in a bore to find it's own center line with the case body (least resistence). I doubt there would be much difference at all. It's not the accuracey of the full length die but the amount it shrinks the case body.

    * benchrest chambers are rarely ever a standard chamber, so that also tells you some things. First in will usually be a very minimum if not undersized chamber (diameters). Secondly the necks are always a "tight neck" setup with about .0015" clearence, and this means a full length die ain't ever gonna work well unless it's made just for that chamber with a minimum resize. But could you do it with a custom built full length die is the question? Yes with the right die. Do you think that the Canadian guy that zapped a dude a half mile away used necked sized brass? About as good a chance as a cube of ice in Hades. His brass was full length sized at the factory before it was ever loaded.
    gary
     
  13. rscott5028

    rscott5028 Well-Known Member

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    Conversely, you should be able to get the same pressure/velocity from a necksized load with a slight increase in powder. ...similar to the whole freebore issue.

    Right???

    -- richard
     
  14. Bart B

    Bart B Well-Known Member

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    I'm pleased to see all the comments. But I want to add one question to think about.

    What forces external to the cartridge position it in the chamber, both when the bolt's closed on it and when the round fires?

    Naturaly, the force applied will move the cartridge in a direction opposite to that of the force. Gravity is one of them.
     
    Last edited: Apr 27, 2012