How Important is Neck Tension?

Written by Sierra Bullets Ballistic Technician Paul Box

One thing that plays a major role in building an accuracy load is neck tension. I think a lot of reloaders pretty much take this for granted and don’t give that enough thought.

So, how much neck tension is enough?

Thru the years and shooting both a wide variety of calibers and burn rates of powder, I’ve had the best accuracy overall with .002″ of neck tension. Naturally you will run into a rifle now and then that will do its best with something different like .001″ or even .003″, but .002″ has worked very well for me. So how do we control the neck tension? Let’s take a look at that.

First of all, if you’re running a standard sizing die with an expander ball, just pull your decapping rod assembly out of your die and measure the expander ball. What I prefer is to have an expander ball that is .003″ smaller than bullet diameter. So for example in a .224 caliber, run an expander ball of .221″. This allows for .001″ spring back in in your brass after sizing, and still give you .002″ in neck tension. If you want to take the expander ball down in diameter, just chuck up your decapping rod assembly in a drill and turn it down with some emery cloth. When you have the diameter you need, polish it with three ought or four ought steel wool. This will give it a mirror finish and less drag coming thru your case neck after sizing.

Expander Ball 2If you’re using a bushing die, I measure across the neck of eight or ten loaded rounds, then take an average on these and go .003″ under that measurement. There are other methods to determine bushing size, but this system has worked well for me.

IMG_6690Another thing I want to mention is annealing. When brass is the correct softness, it will take a “set” coming out of the sizing die far better than brass that has become to hard. When brass has been work hardened to a point, it will be more springy when it comes out of a sizing die and neck tension will vary. Have you ever noticed how some bullets seated harder than others? That is why.

Annealling at Sierra BulletsPaying closer attention to neck tension will give you both better accuracy and more consistent groups.

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15 Responses to How Important is Neck Tension?

  1. Pingback: How Important is Neck Tension — Sierra Bullets | Rifleman III Journal

  2. Daryl says:

    All good points and all things that I do. I see you use a Giraud annealer, I use an Annealeze but any annealer with an adjustable dwell time is good. The old school method of standing cases in a pan of water and heating the necks with a torch and knocking them into the water…. isn’t. In fact, it’s scary.

    Consistent and repeatable neck tension (with properly annealed brass) is a big key to accurate groups at distance Myself, I prefer to remove the expander ball entirely when sizing fired (and annealed cases and jut work the brass one way as the bushing contracts it to your desired degree of neck tension…. With this caveat.. The brass I’m reloading stays with the rifle it’s loaded and fired in, always.


  3. Mike P says:

    Wishing that I had an annealing setup like yours! Any chance that we can see some video of it in action?


  4. Daryl says:

    If it is a Giraud…and it sure looks like one, you can find a video of it, in action on the Giraud website… Annealeeze also had a video on their site as well

    Myself, I use the Annealeeze, same principle, smaller capacity. Giraud is coming out with an induction setup that eliminates the torch head entirely, if you have the money…..

    Giraud also produces a very nice case trimmer, also expensive.

    Liked by 1 person

  5. Daryl says:

    They produce some nice reloading tools. I like his induction setup but I’d have to be running way more cases than I do now to justify one.

    I take it (hopefully) that you use Templac as a temperature indicator as well. Fine line between too soft and not annealed at all.

    I’ve seen some interesting (and dangerous) annealing methods on You-Tube, including the tip over in the pie pan with water method.

    have fin and don’t burn your fingers….lol


  6. Daryl says:

    I have those Redding bushing boxes too. I make my own as needed however. Dang bushing are expensive and it’s so easy to bore and ream to the size I require. I use oil hardening ground drill rod blanks. A stick goes a long way….

    You have my curiosity aroused Paul… I see you are using Redding dies. Ever try John Whidden bushing dies? I use his meplat pointing dies and his bushing dies as well.

    Your *Sierra’ meplats definitely need pointing btw. I’ve actually uniformed meplats in Sierra pills, chucked in a collet in a lathe and angle turned to uniform the business end. BC is everything.


  7. firstriverbend says:

    For all those whom feel annealing with the very old method of heating brass and tipping it over in water is scary or in some manner dangerous, you really need to read this article from Sinclair International.

    Are there better methods currently available, yes. Will the old methods work, YES!
    There is nothing dangerous, nor scary about the water tipping method if done correctly and one wears proper safety equipment, but then everyone knows it is not safe to reload, without all of the proper safety measures in place and one of those is safety glasses. Isn’t it???

    It is entirely possible to get very good results with the water pan method, but it does take a bit of skill.
    If one has the timing set incorrectly on the machines, you will have a lot of ruined brass too.
    Reloading is a skill intensive action. Poor skills, careless skills and you will have a poor, to dangerous experience every time.
    Just something to remember. 🙂


    • Densi stanley says:

      I have an old rectangular steel fry pan and stand cases in there and heat and knock over. find it better to under heat than over heat the brass and anneal every 3 or 4 reloads. Thats for my 6,5×47 L . 308 not so often, after many dozens of reloads of 222 rem I felt guilty and after 20 odd years annealed them.
      I do not run hot loads. I find a load that shoots very well consistently at a lower velocity. For last 25 years .222 rem is 21.5 gns bm1 and sierra 52 gn HPBT help me win 100y and 200y shoots against, on the day, ALL comers. So I win when the others have a miss. A lot of 10 x 10s is better than 9 x 10,01 and a 9.01. Wins every time.
      I dont want to win every time just push the other shooters. Im 74 and been shooting and reloading for many years.
      Over many years I learned Care and patience make good reloads.
      Very Good rifles and scopes and if i miss it was ME .
      For new reloaders . if you want to know how your rifle shoots give it to the best shooter in the club with a box of factory ammo and ask them to shoot it. If they shoot well then you can aim to do as well.


  8. David Ruppel says:

    Good info. Thank you!


  9. firstriverbend says:

    Have been reading Hatcher’s Notebook, by Major General Julian Hatcher. A very interesting and worthwhile read. On page 207 he is talking about the problems and testing of brass, describing what happens when brass is too soft, etc…
    Hatcher was an amazing person, not afraid to mention his own mistakes and laugh about them when appropriate. One thing he talks about is the how and why of making brass correct for use in cartridges. He describes the method used for annealing brass, where by it is heated at the neck, with the head standing in water and then tipped in. 🙂
    Would appear this method has been used for longer than I realized.
    Once you read about how dangerous it is to have the head of the brass too soft, you will tend to shy away from other methods of annealing, where the head is not protected from overheating and becoming too soft.
    Turns out a piece of brass with too soft a head is a certain method of destroying a firearm!!
    So I will continue to re-anneal my with a safe and certain method approaching 100 years of practice, thank you very much.
    Seems the idea of using water to control the temperature of the head of the case has a great deal of merit going for it. The idea of having a breech disassemble itself because the brass was made too soft, is not something I would like to explore.


  10. Morten Breiland says:

    So for example in a .224 caliber, run an expander ball of .221″. This allows for .001″ spring back in in your brass after sizing, and give you .004″ in neck tension.


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