Neck Tension on Bullet

Discussion in 'Reloading' started by Reloader222, Apr 15, 2013.

  1. Reloader222

    Reloader222 Well-Known Member

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    When sizing cases it is said that you need to size the case inner dimensions at least 0.002” less than caliber as to maintain a proper tension on the bullet. Some experienced reloaders say you must throw out the expander/decapping rod when resizing since it tends to throw out the alignment of the case neck. This is working very fine with my .222 Rem since the sized case is between 0.002” and 0.003” under caliber after sizing. I have tested load on this sizing technique and could not find any difference in pressure or grouping of the .222 Rem.

    However, when it comes to my .270 Win it is a totally different story. When I take out the expander/decapping rod, it gives me a measurement of the inner dimensions of up to 0.007 - 0.008” smaller than caliber. I use a Lyman VLD deburring/camphering tool. My question is whether the tension is excessive and what influence it would have on consistency of loads?
     
  2. Kevin Thomas

    Kevin Thomas Well-Known Member

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    Reloader222,

    This is where the Type-S or other bushing dies shine, and their real reason for existing. Brass neck thicknessess vary considerably from brand to brand. The only way the die makers have to deal with this is to size the necks down excessively, then open them back up to proper I.D. with an expander ball. Sounds like your 222 worked out pretty well in this regard, but that's really just a matter of coincidence. In the 270, you're seeing the more typical result, and that's where the excessive neck tension is coming from.

    The bushing dies allow you to select a bushing that reduces the O.D. to the correct dimensions that the end result is the correct I.D. for whatever caliber you're dealing with. Works very well, and again, it often requires several different bushing sizes for a given caliber, depending on which brand of brass is being used and its particular neck dimensions.

    Go to the bushing dies, and select a bushing that's about .002" under the measured O.D. of a loaded round with that brass. That's a good place to start, and a little fine tuning may help accuracy. Just understand that you may need several different size bushings, if you're using several different makes of brass. All part of the process, but that should solve the problem.
     

  3. Hunter2678

    Hunter2678 Well-Known Member

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    As Kevin stated the bushing style dies are the way to go. I use the redding type S bushing dies for my 6br with superb results. A turned & loaded 6br round for me has an OD of .268 on the money so my .266 bushing is what I use. I also have the .267 and .268 bushings just to be safe. I also like to take it a step further and turn all my lapua necks in order to minimize that as a variable affecting accuracy as well... the lapua brass is very consistent and usually all I ever need to remove is maybe a half thou of neck thickness from them just to remove any of the hi spots.
     
  4. Mikecr

    Mikecr Well-Known Member

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    'Tension' as it relates to bullet 'grip' amounts to brass springback. That is, the neck springing back against a seated bullet.
    Your sizing provides influence over springback, but eventual rather than direct. And since there are currently no tools available to measure neck springback back force, it would be difficult to know directly if your 270 necks are actually gripping bullets with more force than your 222.

    What you will notice directly is that bullet seating force is excessive with your 270, without the expander, because your bullet is now providing that function. Those necks are going to be expanded one way or another, and bullets are probably the very worst of expanders made.
    Also, your 270 OgvOAL as loaded with so much seating force would be all over the place..

    Necks should be expanded before bullet seating(for several important reasons). If you want better expansion than provided by your die, use a Sinclair mandrel expander in a separate operation.
     
  5. OKIE2

    OKIE2 Well-Known Member

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    Lee neck sizer die is better idea than bushing die
    you only need one die for any & all brass.
     
  6. Kevin Thomas

    Kevin Thomas Well-Known Member

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    OKIE2,

    Having some level of control, with the option of going stronger or reducing that tension is the point behind the bushings. Yes, they're a bigger investment than the Lee stuff, but I like to keep the options open, and be able to exert that control as the situation dictates.
     
  7. MTBULLET

    MTBULLET Well-Known Member

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    I control the tension using lee dies by changing the dia. of the mandrel if needed.
     
  8. Mikecr

    Mikecr Well-Known Member

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    Your missing the fact that tension, or grip in this case, is not purely a matter of neck diameter.
    It is springback force to area applied.
    So to adjust tension you increase area of the bullet -springback squeezed by the neck.
    You do this by seating bullets deeper, or adjusting the length of sufficient sizing. This is where bushings provide a great advantage in reloading & load development. You can adjust the length of sizing to your necks.

    I measure seating force with a hardened mandrel in every neck before bullet seating. With this, and an adjustment to bushing dies(I use Wilsons), I can match necks. Every single one.
    I've seen with minimal sizing that tension does not change with reloading cycles. It's only with excess sizing that reloaders are left with ever changing tension and annealing cycles to alleviate(very poor 'fix').
     
  9. jfseaman

    jfseaman Well-Known Member

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    Consistent annealing
    Concentricity
    Consistent neck wall thickness

    I have a regular schedule for annealing brass, different for each caliber but I try to stick to it.

    I now use Lee Collet dies as I get very good concentricity and tension

    I turn the necks of pretty much everything.