New RCBS Dies ... now shaving bullets ... ?

Discussion in 'Reloading' started by Gettn2, Mar 28, 2009.

  1. Gettn2

    Gettn2 Active Member

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    In playing with my 204, I purchased some new RCBS dies. (Should have used Redding : ) I am using Rem brass and for some reason I cannot get the resizer to give me anywhere close to the proper neck tension. I prefer .003 and am getting close to .006 tension. With the neck tension at .006 I am slightly shaving bullets. Has anyone else had this problem?

    My bullets measure exact at .204 and the expander ball is measuring .201 but when I resize ... I end up with a .198 diameter. Is the resizing die making the neck to small and the brass is not responding to the expander ball?

    If you have any ideas ... please respond.
     
  2. woods

    woods Well-Known Member

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    What you are seeing is springback. When the expander goes through at .201" the brass springs back the .003" to .198" (that does seem like a lot). Springback will lessen as your brass neck work hardens. The amount of springback will lessen with additional firings.

    Are these new cases or once fired?

    The other options are to go to a Lee Collet Neck Sizer which presses the fired neck inward and so springback will spring the brass back out and give you less bullet grip. Perhaps too little.

    Or you can get a bushing die and several bushings to size your neck to the grip you want. However, IMO, the bushing dies work best when you do not use the expander supplied with it and you neck turn your brass so any inconsistant neck thicknesses are outside neck turned off. That way when you size the outside of the neck with the bushing the inconsistant neck thickness variations are not just pushed to the inside.
     

  3. Gettn2

    Gettn2 Active Member

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    I have tried both once fired and new and they both end up the same. I am a fan of bushing dies, and should have done that in the first place.

    I may try your suggestion of turning and see what happens. Appreciate your suggestions.
     
  4. Winchester 69

    Winchester 69 Well-Known Member

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    Post deleted.
     
    Last edited: Mar 29, 2009
  5. gray wolf

    gray wolf Active Member

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    Hmmm?
    I could be wrong here but I thought that brass after repeated firring or sizing
    gets work hardened and that is what creates spring back. Isn't that why we anneal our brass? Anyway the gentlemen Say's it is with new and old brass so lets forget the spring back for now.
    RCBS dies have gotten a bad rap from some folks. I think in many cases justified. I would say it is possible that your die is a little undersized making the cases a little to small AND your expander button may be a little undersized also. ---.201 on the ball sounds like it may be little small.
    Don't get mad but you say you are into bushing dies and are capable of neck turning--so may I ask why you would want to use a nasty expander ball ?
    Any way--RCBS has great Cust. service and would replace the dies if they are wrong.
    Just trying to help.
    .006 on the neck tension is not that tight --a little yes but should be doable
    But if you prefer .003 then that is what you should have by all means.
    That is why we reload--I like .004 two thou per side. I am sure you have chamfered the inside case mouth (just checking) One last thought are you using the rcbs seating die? Who knows it could have a problem.
    If you are shaving bullets it can't be helping your run-out.
    GW.

    I just grabed a die and checked the expander ball. It is a Redding 270 die and the ball is .276.
    Bullet is >277
     
    Last edited: Mar 29, 2009
  6. boomtube

    boomtube Well-Known Member

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    Your expander ball is too small. It should be .204", or not less than .203". Call RCBS for a new one.

    And your case mouths should be champhered to ease bullet entry without shaving the heels.

    What's real bullet "tension"? Actually, what many of us call tension is only the undersized, or what engineers call an "interference fit" between two diameters. In our case (litterally) the neck and bullet diameters are an interferrence fit and that's only casually related to real bullet tension. But, using the common term, the neck fit should only be 1 or 2 thousants undersized, no more, so a proper expander ball should be bullet diameter or 1 thou less, no smaller. With typical spring back that will give an interference fit of 1 or 2 thou, which is plenty to hold the bullet securely without excessivily working the brass.

    When the necks are expanded - stretched - more than about 2-3 thou (it varies a little with caliber), it exceeds the elasticity limits of brass. The stretched brass will only spring back about 2 thou. no matter how far we expand it. Thus, when seating a bullet in a neck that is more than 3 thou smaller than the bullet, the bullet simply acts as an expander. So, even tho your bullets are stretching the necks more now, there is no more real tension than there would be with a properly sized expander ball.

    You need to decrease the interference fit of your bullets, they are fixed so you must work on the necks. As you are finding, excessivily small necks greatly increase the probability of damage to the bullet's heel as it enters the much too small neck. AND, the excessive seating force tends to push bullets off axis and increases bullet run-out. Neither situation is good for accuracy.

    Any cartridge brass will have, or certainly needs to have, "spring back". (For one thing, that's what allows us to extract the case easily after firing!) How much springback we get varies somewhat by the alloy but some is always there. Hard brass does have more spring back than soft but hard is also more brittle and prone to split. We anneal to keep the neck spring back in the proper range for best bulllet fit/tension AND to reduce premature splittling.

    Improper annealing by overheating the necks to a red heat, a very common occurance with most inexperienced reloaders, will reduce neck springback to virtually zero. Excessive neck softness destroys any real bullet tension, no matter the amount of diameter/interference fit of the necks.
     
    Last edited: Mar 29, 2009
  7. Gettn2

    Gettn2 Active Member

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    Thanks guys ... I will get this all figured out this next week. I appreciate the tips.