Bumping the Shoulder Question

Discussion in 'Reloading' started by samson, Nov 17, 2008.

  1. samson

    samson Well-Known Member

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    I had some brand new Norma Brass in a 300 WM and have since fired them once. I will be using a Redding Body Die and a Lee Collett Neck sizer. I was told that I should only bump the shoulder back about .001 to .002. How is this done and do you think that my accuracy will get better since it has been sized to my chamber?
     
  2. EddieHarren

    EddieHarren Well-Known Member

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    Seeing as the brass has been fired in your chamber, you need some sort of device to measure the length of your brass from the head to the shoulder. I believe that Hornady offers such a tool mounted on a dial caliper. Once you measure you can then set your FL sizing die to only move the shoulders back .001-.002". I can't say that accuracy will benefit but, your brass will last longer. When I chamber a rifle for a customer I always include a small piece of barrel with the neck and shoulder area cut in one end. This widget can be used to measure the amount of bump.
     

  3. old_heli_logger

    old_heli_logger Well-Known Member

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    If it's a bolt action, I'd just neck-size it...unless you're having problems chambering the reloaded round. Your brass will last longer since it's fire-formed to your chamber and it should be more accurate. Please correct me if I'm wrong...
    Good luck!
     
  4. samson

    samson Well-Known Member

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    Old Heli Logger, With norma Brass, how many firings can I expect to get before it starts to get a bit tight to chamber? I do also have some sort of body die that sizes just above the belt if it starts to get fat. (By the way, it is a bolt action.)
     
  5. woods

    woods Well-Known Member

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    Hey samson

    Hornady makes a head and shoulders gauge

    MidwayUSA - Hornady Lock-N-Load Headspace Gage 5 Bushing Set with Comparator

    It clamps onto your caliper and you take measurements close to the datum line on the case

    [​IMG]
    [​IMG]

    Your case will most likely not expand enough with one firing to get a crush fit in the chamber. On a 300 win mag I own I get the following measurements during the firing cycle:

    New case - 2.253" (subtracting the 2" for the gauge and the measurement itself is not important, only it's relationship to the other measurements)
    Once fired - 2.270"
    Twice fired - 2.272" (slight crush fit)
    3 times fired - 2.2725" (crush fit and time to push the shoulder back)

    So I neck size only with a Lee Collet for the first 3 firings and then push the shoulder back to 2.272" with a Redding Body Die for a slight crush fit. You will have to push the shoulder back each subsequent firing after.

    Note that almost all the expanding happens on the first firing but the case has not been through it's full cycle of expansion. A caveat to this is that if you size the body and not just neck size then when the die squeezes the case body it will push the shoulder forward just a little. IME not enough to make it have a crush fit and it will not be consistant.

    When sizing, set your rifle up in a vise and chamber the round as you go through the sizing process and it will tell you when you are developing a crush fit. Until you do, neck sizing will be sufficient.
     
  6. samson

    samson Well-Known Member

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    Woods,
    I noticed that when I took an old case that was a crush fit and ran it through the Body Die, It did push the shoulder forward and not set it back. What do I do then?
     
  7. woods

    woods Well-Known Member

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    Thread the die in a little further, resize and try it again in your gun. Keep doing that until you feel the case become easy to chamber. I like a very slight crush fit in my loads.

    When adjusting the die move it a very little. I find it advantageous to make marks with a magic marker on the die, lock nut and press

    [​IMG]

    In this photo the difference shown between the marks on the lock nut and die threads can move the shoulder back .002" which is about the amount needed to take a case from a crush fit to no shoulder contact. Sometimes it takes forever when zeroing in on the exact die adjustment and you may have to adjust in bigger turns and go past the point where you push the shoulder back too far and then trash that case, then go back to find the exact point of a slight crush fit.
     
  8. samson

    samson Well-Known Member

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    Thanks for all your help.
     
  9. lever-hed

    lever-hed Well-Known Member

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    I had the same trouble on the redding body die also. It took me a little while getting the right adjustment, when sizing the body the shoulder pushes up slightly, and even trashed a few shells because I lubed the shoulder. Overall, it worked out, once I got the hang of it. I've been using the RCBS micrometer to measure the headspace. Its a little pricey at $45 but works well and I find I use it constantly and also measures oal to ogive/seating.
     
  10. old_heli_logger

    old_heli_logger Well-Known Member

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    The number of firings before you need to bump the shoulder depends on how hot you're loading your ammo. I run moderate loads in my 7mmRM and I'm ready for new brass before I need to bump. Usually 5 or more loadings. I use low-end brass; what can I say, I'm frugal. I've never tried annealing the necks, but I'd like to sometime...
    Good luck!
     
  11. Delta Hunter

    Delta Hunter Well-Known Member

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    I really, really suggest getting the headspace gauge like woods has in the picture. I didn't realize until I bought one that I was pushing shoulders back way too much.
     
  12. dmgreene

    dmgreene Well-Known Member

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    Samson I have been using the Redding competition shell holders. You start off with a case that has been fired enough times to the point that it is difficult to chamber. Then start with the shortest shell holder (-.010) and resize the case. If it doesn't chamber then use the next size up shell holder until the case will chamber. They are in .002" steps from -.002" to -.010". I like this method the best, especially if you are loading the same caliber in two different guns. You can just swap shell holders to match the headspace for each gun without having to mess with the lock ring on the die and losing your initial setting.

    David