7mm jrs

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by meatyrem, Jan 28, 2012.

  1. meatyrem

    meatyrem Well-Known Member

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    I was curious about what case is used to form the 7mm jrs. I read that the 280 case would be dangerous to use for this cat. What is the appropriate case to use?
     
  2. KRP

    KRP Well-Known Member

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    What is the danger in using 280 cases? The JRS is just an improved version of the 280. You should be able to form it from any '06 based case with the 270 or 280 brass providing a longer neck.
     
  3. meatyrem

    meatyrem Well-Known Member

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    Loaddata.com indicates that it is not possible to use 280 cases and fireform in a JRS chamber. It says that it is very dangerous to do so because of the 35 deg shoulder is 0.050 further ahead than the 280 improved. I like the sounds of this round. It it may be a lot of work to get it
     
  4. KRP

    KRP Well-Known Member

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    How else do they form cases? I think the confusion is that the term improved is often automatically associated with the name Ackley. PO designed his improved chambers with the thought of being able to safely fire standard ammo in them, many others didn't. It's not the case that's the concern with the JRS...it's standard ammo. I've never used anything but 270 brass in my 280AI so the shoulder moves forward ~.050" on the first firing. Put a false shoulder on the brass to keep the case head snug against the bolt face and then shoot it. Others use a bullet with a significant jam into the rifling to do the same, I haven't had as much luck with this method. Gibbs rounds move the shoulder forward ~.200" and it's not a problem when done correctly.
     
  5. KRP

    KRP Well-Known Member

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    I went and looked at loaddata.com and the warning is specifically about 280 ammo, not the 280 case.
     
  6. meatyrem

    meatyrem Well-Known Member

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    So then it is ok then after it is already formed into 280 AI to form into jrs? It has to be done in steps then? I read somewhere else that there would be head space problems if it were regular 280 cases, but then for 280 AI it is ok to fireform into JRS? I hope I'm understanding this correctly. So to be simple you could get 280AI brass then fire it in a JRS?
     
  7. Sennaspeed

    Sennaspeed Well-Known Member

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    280AI brass cannot be fireformed as is in a JRS chamber.

    You'll need to form a false shoulder on the case before it can be safely loaded and fired.
    To form a false shoulder you'll need to neck the case up to say .30 caliber and then begin necking back down with your JRS FL die until you neck enough of the case that the false shoulder is holding the casehead against the boltface.

    You then size all your cases like this, load a moderate to high load and fire away.

    You'll have perfect JRS cases when you're done.