7mm rem mag case capacity vs same load make a difference?

Discussion in 'Reloading Forum (All Calibers)' started by rockwind1, Sep 19, 2018.

  1. rockwind1

    rockwind1

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    hi, i have found a good load of 67.3 gr h1000 for my 7 rem mag using my brand new unfired nosler brass. getting decent es and sd and good groups. however, after firing, the shoulders have reappeared about 20 thousands higher on the case, obviously creating larger case capacity. is that case capacity going to make any significant difference when i go to reload the fire formed cases? as far as MV? do i have to "find the node" again, so to speak, or can i just happily use my same load and expect same results with perhaps even better es/sd since the cases are fireformed? apologies in adavance as this may be a newbie question, I am a belted magnum virgin.
     
  2. #40Fan

    #40Fan

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    Your brass has changed, so will everything else.

    But, you never know. Might be for the good!
     
  3. CaptainMal

    CaptainMal Silver $$ Contributor

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    Headspace off the shoulder and keep the case the same each firing. If it's moving that much on the first shot it may continue at a lesser rate and be tough to chamber.

    Now go shoot the once-fired cases and see if you can detect a change.
     
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  4. JohnKielly

    JohnKielly Australia, not Austria Silver $$ Contributor

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    Don't belted cases headspace off the belt, hence the probability that they couldlengthen first firing?
     
  5. rockwind1

    rockwind1

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    thanks for all the input. i will see what happens
     
  6. M-61

    M-61 "Quis Separabit" Gold $$ Contributor

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    Yes they do. Then after 1 or 2 more firings they are headspacing off the shoulder, the same as beltless cases. Caution: if you get into 'bumping' the shoulder back the case will grow every firing, leading to possible separation at the head. That brass has to come from somewhere.

    As said above by CaptainMal headspace off the shoulder.
     
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  7. Dusty Stevens

    Dusty Stevens COVFEFE- Thread Derail Crew Gold $$ Contributor

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    I try to stay away from belted cases for exactly this reason. Most regular ole dies cant bump the shoulder without bottoming out too hard on the belt
     
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  8. thatguyshm

    thatguyshm

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    Post back with results, I'm using 67.5gr H1000 and my shoulder changes 0.016" from new to once fired. I only have about 65 left before all the new brass is once fired. I ran mine through a .308 sizing button before necking back down, mainly shoulder growth on my cases. I'm getting an inch at 450 yards so I don't want to mess it up too much.
     
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  9. AckleymanII

    AckleymanII Gold $$ Contributor

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    I shoot Remington brass in my 7 Mags. I full length size on every firing only because this is where I get my best accuracy, which may have something to do with consistency of the internal capacity of the case.

    Most of my loads are running on the Max side, where the accuracy nodes are with 120,140,150, 154,162, 168's.

    As most of my accuracy loads are in the 60K-65K area, neck sizing 7 Rem Mag brass has driven me crazy since 1978 when I got my first one. There must be considerable difference between F.L. sized brass and Neck sized brass. Just my dumb luck to get the best accuracy at a Full Length sized internal capacity that stays constant instead of variations of Neck Sized cases with their corresponding internal capacities. It is aggravating to have to full length size a case when you have just got the case fully formed.


    My best accuracy were very small groups abound are always full length sized. The issue of fire forming after a full length sizing had me chasing my tail for a while. So, I prep 100 cases for each 7 Mag I own, and they are in a case guard 100. I go through the 100 pieces of brass in succession, and I do not just choose 20 and shoot them up till they are worn out.

    Learning to set the full length sizer to match the chamber with the brass is critical for best brass life.

    We all know that there are two dimensions that we deal with, which is the dimension at the web and the dimension at the shoulder. Brass for this very, very intense cartridge does not have long the case life, but does increase with annealing.

    I get around 900 or so rounds on a 7 mag barrel, then it gets replaced with another barrel and another set of new cases....life is easier with this method.

    Rockwind, your experience maybe different from mine.
     
  10. rockwind1

    rockwind1

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    i have not done enough yet to have a firm answer and would really like to hear more about setting your fl sizer to match the chamber, could you elaborate.
     
  11. 270WinDude

    270WinDude

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    ... In theory yes, the pressure difference between those 2 load scenarios will change given the extra case capacity, also possibly some less significant changes in harmonics (?) especially with that much change. In practice, only you can find out. The experienced assumption also points towards a difference. As Ackleyman pointed out, a good option would be to FL size or run 2 batches side by side, on FL sized the other neck. Do you anneal? Are you set up for it? I ask because if you don't your neck sized brass is only going to hold up for a handful of shots anyway before neck tension gets a little problematic IMO which kind of takes away some of the assumed advantages to fire forming in the first place. Very good question though. My opinion is if your not annealing just FL size and don't look back, otherwise experiment.
     
  12. Lougler

    Lougler

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    Will you have to “find the node again?” Yes. Whatever powder charge gets you to the velocity you were at during fireforming should put you back in the game.
     
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  13. Uncle Ed

    Uncle Ed

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    Rimmed and belted cases date back to a time when manufacturing methods and tolerances were sloppy at best.

    Below on the left a newly manufactured .450 Martini cartridge next to a cartridge made during the 1879 Zulu wars.

    [​IMG]

    Below a new unfired .303 British case in a Wilson case gauge, the shoulder location is approximately 1/4 inch shorter than the chamber.

    [​IMG]

    Below a fired case in the Wilson gauge and the amount the case is sticking above the gauge is how much longer the chamber is.

    [​IMG]

    I grew up reading Jack O'Connor hunting stories so I know the .270 Winchester is the worlds best non-belted magnum. ;) Bazinga
     
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