proper amount of neck tension

Discussion in 'Reloading' started by dmax1800, Sep 1, 2013.

  1. dmax1800

    dmax1800 Well-Known Member

    Messages:
    170
    Joined:
    May 8, 2013
    I've done some searches and can't find the answer to this question.

    I'm loading for a 300 win mag and a 270 win with Norma brass and RCBS FL dies. The expander ball measures .3050" for the 300. I'm measuring neck tension by measuring the case mouth before and after seating the bullet. I'm getting .0020 to .0025 on both once fired brass and brass that has been fired 14 times and annealed 3 times. My gunsmith says that for my bolt action hunting rifle I need .004 to .005 to hold the bullet in place against accidental jars.

    What do y'all think is the proper amount of neck tension???

    Thanks.
     
    Last edited: Sep 1, 2013
  2. AZShooter

    AZShooter Well-Known Member

    Messages:
    2,071
    Joined:
    Dec 12, 2005
    Most of the RCBS dies I bothered to measure yielded a .003" for difference between sized and loaded. Many handloaders will use .002" which can be done with a Redding S bushing sizer die. Some even use .001" or less but that is ammo not meant for a magazine.

    I can't imagine wanting to go tighter than .003" for tension unless the rifle had recoil so severe that the rounds in the magazine experienced bullet setback. At that point a crimp is the more common solution rather than more neck tension.

    I have read more than once that high neck tension could lead to misalignment of bullet causing poor accuracy.
     

  3. MagnumManiac

    MagnumManiac Well-Known Member

    Messages:
    1,002
    Joined:
    Feb 25, 2008
    I am a firm believer that no cartridge requires any more neck tension than .002", even heavy kickers.
    On my comp rifles and some of my very accurate hunting rifles I run .0015" neck tension , this includes my 338WinMag, never had any bullet setback during recoil and they're not crimped. The most important factor, especially with the 300WinMag, is that the neck tension is consistent across all cases. I anneal every other shot with my 300, but this is a target rifle, in my hunting rifle I only anneal whenever the brass needs trimming.

    Even my 375 Weatherby and 416Rigby only get .002" neck tension, the Rigby gets a crimp but the 375 doesn't.
    As a side note, a few years ago I bought some old Kynoch 416Rigby ammo, not sure of it's age at the time, but the ONLY thing holding the bullets in the necks was the case mouth where it had been rolled into the cannelure! I pulled them all, resized the necks and reseated the pills, and they shot quite well.

    Cheers.
    gun)
     
  4. Mikecr

    Mikecr Well-Known Member

    Messages:
    4,249
    Joined:
    Aug 10, 2003
    Your gunsmith doesn't know what he's talking about, and I wouldn't be surprised if he's making more than that up as he goes..

    For one, you cannot produce more than ~3thou of tension, regardless of sizing. That is all necks will spring back. Even very thick & hard necks.
    When you size necks down more than this, bullet seating(with excess seating forces) will just size the necks back up, and the same spring back(as you would have without the oversizing) grips the bullet.

    Necks won't ever spring back 4-5thou.

    And when someone suggests that annealing will increase your tension, go ahead and tell them they don't know what they're talkin about. Annealing reduces springback, which is all that holds a bullet.
     
  5. jfseaman

    jfseaman Well-Known Member

    Messages:
    3,591
    Joined:
    Apr 8, 2012
    I'm wondering of the obvious was missed.

    Is it .002 on radius or diameter.

    Example: all my 30 cals have an internal neck diameter after sizing that is .304. To me this is a .002 per 'side' neck tension. I check this often as it is not something I want varying much.

    Your gunsmith may mean exactly as my example shows. An internal diameter .004 or .005 less than bullet diameter. For general loading, my instructor/mentor, reading and practice leads me to that standard measure.

    For special forms of shooting, a neck internal diameter after sizing that is as 'low' as .002 less than the bullet diameter seems to work for some. Usually described around the same prose as 'tight' necks and 'match' chambers where neck turning is required.
     
  6. dmax1800

    dmax1800 Well-Known Member

    Messages:
    170
    Joined:
    May 8, 2013
    Its .002 diameter. I measure the diameter of the case mouth before and after seating the bullet. The difference is usually .0020 or .0025. Still no where near the .004 to .005 that he is talking about.
     
  7. Broz

    Broz Well-Known Member

    Messages:
    8,636
    Joined:
    Feb 3, 2007
    This statements needs to be further clarified Mike. I agree with you, but it also needs to be noted that when using a bushing die, and only down sizing .002 after a few firings the brass hardens and neck tension will be lost from added spring back. The cure is to either drop down in bushing size or anneal the brass to return it to it's original softer state.

    My first hand example is this: 338 LM in Lapua brass. Great bullet hold with a .366 bushing. After 4 firings some of the bullets were loose. This indicated loss of neck tension as well as inconsistent neck tension. I dropped to a .365 bushing and they were all tight again. At this point I bought my first annealing machine and annealed this same brass. I returned to using the .366 bushing and all was tight again.

    The problem I seen with dropping a bushing size was that not all cases needed the smaller bushing. This was proof to me that I indeed had inconsistent neck tension. I find that annealing more often keeps all the necks at the same hardness and allows me to run the lighter tension I desire and still hold all the bullets the same.

    Jeff
     
  8. Mikecr

    Mikecr Well-Known Member

    Messages:
    4,249
    Joined:
    Aug 10, 2003
    Good way to clarify Broz. But there is still more to it.
    Some see your annealing adjustment as regaining tension, when it's actually reducing springback. And while your adjustment regains the desired interference fit, tension out of this is still reduced.

    Your annealing adjustment falls apart on expansion, and you will expand, even if it's done with bullet seating only. That's when reduced springback from annealing leaves less tension than using a bushing adjustment.
    The REAL problem adjusted for here can be better addressed directly: Stop changing springback(another thread).

    It's important for folks to know that the only thing gripping a bullet is springback, and there are limits to this.
    Your set interference fit only needs to include the neck's springback, because that's all the grip you're going to get anyway. More down sizing is just overworking neck brass(changing springback, leading to adjustment/tail chasing).

    Try this;
    Size necks varying amounts leaving >3thou under cal as measured, seat bullets & again measure neck diameters, then pull them, and measure the springback from seated neck diameters. It's always gonna be 1-3thou, and this is all that ever grips a bullet.
    If you anneal one of these necks and do the same test, you'll see less springback from it than non-annealed necks.

    jfseaman, your 4thou interference fit does not represent 4thou of tension. If you sized your necks down 10thou under cal, it would not mean you have 10thou of tension. It only means 10thou interference fit for bullet seating, which would cause very high bullet seating forces(because you're using your bullets as an expander), but no more tension at all.
     
  9. Broz

    Broz Well-Known Member

    Messages:
    8,636
    Joined:
    Feb 3, 2007
    Agreed Mike. But the problem I want to deal with is the fact that not all brass hardens at the same rate. Thus why some of the bullets had tension some did not, before annealing. So I anneal in a effort to keep the brass equal in spring back case to case.

    In the end there is more than one way to skin the cat. One can beat any method to death. But what I have done is developed a method that has shown me results worth repeating my ELR groups. I have kept track in the log book for a long time to get multiple data samples. I am confident in saying this method works well for me in the type of shooting I do.

    YMMV

    Thanks
    Jeff
     
  10. jfseaman

    jfseaman Well-Known Member

    Messages:
    3,591
    Joined:
    Apr 8, 2012
    OK. Not well just now, flu. But I'll do all the normal 'prep', seat a bullet, pull it then remeasure ID.
     
  11. jfseaman

    jfseaman Well-Known Member

    Messages:
    3,591
    Joined:
    Apr 8, 2012
    Was feeling better this afternoon so went to the shop. 30-30 was in the reload queue so went with that. Checked the 308, 300WSM and 300RUM that were part way through but up to at least the sizing point and all ID were the same.

    Measured with a dial micrometer not digital.

    Sized case:
    ID .304
    OD .324, the FC 30-30 case had a measured thickness of .010. I have 3 tools for this including a laboratory grade tubing tester.

    Seated bullet
    OD .326

    After bullet pulled:
    ID .305
    OD .325

    Resized case
    ID .304
    OD .324

    Bullet diameter before and after was .308.

    So...

    Per Mikecr that is a .002 neck tension.
     
  12. Mikecr

    Mikecr Well-Known Member

    Messages:
    4,249
    Joined:
    Aug 10, 2003
    Close, but,,
    Your carefully measured neck thickness of .010 wrapped around a bullet measuring .308 = .328 loaded neck OD (not .326).
    If it sprang back to .325 after pulling the bullet, that's .003" of tension.

    No combination of your reported measure results in .002 neck tension.
     
  13. jfseaman

    jfseaman Well-Known Member

    Messages:
    3,591
    Joined:
    Apr 8, 2012
    Now I understand 'neck tension' but wow Mikecr

    from my point of view your style of communications is insulting and incendiary.

    How old are you?
     
  14. Mikecr

    Mikecr Well-Known Member

    Messages:
    4,249
    Joined:
    Aug 10, 2003
    You've challenged my communications several times now(several threads), and with little more than generalizations, errors, and insults.
    But we're getting along just fine. I am glad you understand neck tension.