Neck bushing dies

Discussion in 'Reloading' started by Natty Bumpo, Jan 21, 2008.

  1. Natty Bumpo

    Natty Bumpo Well-Known Member

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    The only dies I've ever used have just been your "plain Jane" 2-die sets from Redding, RCBS, Hornady, and Forster. But if you had a rifle capable of 1/2 MOA precision, would there be an advantage to using one of the neck-bushing dies. I don't know a lot about them, but as I undertand it, you insert a different sized bushing, depending on how far below bullet diameter you want to constrict the neck. This affects how much tension is holding the bullet in place. I guess if all your bullets are held to the same tension, they'll all leave the brass at the same pressure.

    Wouldn't my plain Jane die apply consistent tension as well, although it wouldn't be adjustable. What's the advantage of being able to play with the degree of neck tension? Wouldn't a pricey seater die that assured good bullet concentricity with minimal runout do more for accuracy?
     
  2. long ranger

    long ranger Well-Known Member

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    Your plainjane dies do exert the same neck dimension assuming your brass is identical. The difference is in you have no say in what that dimension or amount of tension is.
    The bushing type dies are used to get optimum neck tension for a particular neck thickness and chamber dimension.
    Differences in chamber size and brass thickness can not be addressed with standard dies as easily as with interchangeable bushing in .001 increments.
    Eg. 308 caliber chamber when firing Lapua brass that has a neck wall thickness of .012, leaves the fired case with a neck dimension of .335 so you would use a .333 bushing.
    If you used Winchester or remington brass you may need a bigger or smaller bushing as the neck wall thickness may be bigger or smaller.
    Your generic dies would have a neck size of .330 to make sure you get tension regardless of neck wall thickness, this can work your brass more than necessary, shortening its life span.
    Differences in chamber specs will also change the dimensions of the fired case hence the bushing diameter will change as well.
    The numbers I used are not necessarily the exact dimensions but hopefully you get the idea
     

  3. uncleB

    uncleB Well-Known Member

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    Natty,
    I think you have a few misconception's on this you say "wouldn't a pricey seater die that assured good bullet concentricity with minimal runout do more for accuracy". A pricey seater die will not improve your concentricity but it wont make it worse. for example if you have a sized case that the neck has .005" run out when you seat your bullet with a "pricey seater die" it will still have .005" runout with a standard seater die and the same case your runout after seating the bullet might be .005" or it might be .006" or.007".

    The .005" runout in the first place comes from the sizing die and most (not all) of the time the culprit is the expander ball. in your "plain jane" dies as you run a case in it gets the neck sized down many thousandth's too far, then as the case is extracted from the die it goes over the expander ball and it stretches the neck back out. It is this oversizing that is the main cause of runout and poor case life. If you use a proper size bushing in a bushing die then runout is insignificant and your brass lasts much longer.
    UB
     
  4. 338hammer

    338hammer Well-Known Member

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    Jan 10, 2008
    Natty you have been given very valuable information from very knowledgable gents.

    ANother opinion which goes along with that already stated is; All of my competition dies have undersized expander balls so that I do not pull the neck forward. I use all neck sizing dies after a case has been fireformed to a particular chamber. If a case neck for whatever has been damaged I cull it as a hunter case and full length size with a standard expander ball.

    Now on a wildcat based on a .014 neck wall thickness that I currently shoot. I recently received a new lot of brass from the same company with a neck wall thickness of .009. Amagine my dismay when the first bullet to seat fell in the case. SO I measured the I.D. of that neck and several others and figured which bushing was required and went back through the lot without the decapping pin in after changing to the required bushing. To date on this method I seldom have lost a case and never have to anneal. I also use sleeved seater dies with micrometer adjustment.

    338
     
  5. long ranger

    long ranger Well-Known Member

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    I forgot to mention the expander ball thing, thanks guys. With the Redding bushing dies you can delete the expander ball all together and I did this years ago, they offer a decapping pin retainer that replaces the expander ball. I suspect RCBS may also have this option, but am not sure.
    There is no need for the expander ball after the casing has been fireformed, unless you ding a mouth.
    Also the bushings are offered in hardened steel, which needs to be lubed or TIN coated in which case no lube is required.
    I use the TIN coated bushing , they are worth the extra few $$ in my opinion.
     
  6. Natty Bumpo

    Natty Bumpo Well-Known Member

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    Thanks for all the advice. You all explained things better than anything I've read in any catalogs or on Redding's website.