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Thread: 6mm Wildcat Brass Dimensions

  1. #1
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    6mm Wildcat Brass Dimensions

    I recently got a Hornady headspace gauge kit and was measuring some 6mm brass based on the Lapua .243 case. The chamber design features a longer neck, blown out body and sharper shoulder. The designer called it the 6 Super BR, but it seems similar to some other long range 6mm designs I've read about. What's really working well for me is I have two rifles with chambers cut with the same reamer and fired brass from both chambers measures to within around .0005" of each other, which is about as accurate as I can measure with my caliper. My goal was to have two rifles that could share the same source of brass. Since it takes many steps to form this stuff and I have a lot of it, that is comforting. Also, the second chamber was the first one I cut myself, and although the second rifle has a barrel nut feature, I think the head space is about right. The original rifle does not have a barrel nut and is conventionally head spaced (2 lug BAT long range bench gun). I probably will segregate brass from one to the other, but at least the possibility is there of interchanging if necessary.

    What concerns me is that, while I was at it, I also measured the die formed brass. Prior to fire forming, that brass is .005" short of the fire formed brass. I'm a little unclear as to how to set up such things, but I have about five hundred die formed pieces that I can fire form. Since the initial die forming happened 5 years ago and the gunsmith has since passed away, I was wondering what the best procedure would be. Usually when fire forming I try to have the bullet a few thousandths jam fit into the lands so the primer is held against the firing pin, but that .005" gap worries me a little bit. Is it common (read safe) for first firing brass to push the shoulder that far forward? I could put some color on the die formed brass, chamber it and look for contact in the area of the neck as the blown out shoulder might not form accurately when die formed. That would be my next step I suppose.

  2. #2
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    One way to deal with your issue is to expand the necks to .25 cal. and then size them so that the false shoulder can be felt when the bolt is closed. Be sure to lube the inside of your necks and remove the lube after expanding.

  3. #3
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    Feb 2006
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    wildcat brass

    RCE1 -

    Howdy !

    You might try to fire-form a couple, using a charge of " Bullseye " cover w/ either a tissue paper wad; or wax plug.
    Fire them off, and see what case oal results.

    Got that tip from a High Power Shooter, and it worked great on some .35 Remington brass I had messed the headspace up on.
    I was able to re-claim all 66 pieces, in that instance. For the .35 Rem application, I was using 10gr Bullseye. YRMV.



    With regards,
    357Mag

  4. #4
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    What I am reading is when you chamber your formed class, you have .005 headspace between bolt face and the face of the case.

    I personally think you are looking for a problem that doesn't exist. Load the rounds with a good tight neck tension, seat the bullet out so it jams into the lands, put a thin coat of sizing wax an the case and fire them.

  5. #5
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    Quote Originally Posted by jackie schmidt View Post
    What I am reading is when you chamber your formed class, you have .005 headspace between bolt face and the face of the case.

    I personally think you are looking for a problem that doesn't exist. Load the rounds with a good tight neck tension, seat the bullet out so it jams into the lands, put a thin coat of sizing wax an the case and fire them.
    I think you're right. That's my plan.

  6. #6
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    One of the first rifles I had made was a 7X57 Ackley Improved on a Mauser 98 action. The barrel company was one of those that advertised in Outdoor Life back in the 70's in about a 2" x 2" ad. I didn't know much about it, but whatever the cost of the chambering was and it wasn't much back then, it cost $5 extra to have it minimum headspaced. Should have spent the $5. I figured headspaced was headspaced. Little did I know. When you fireformed 7x57 brass in it, it would separate at the case head. I moved the shoulder back on .30-06 brass and trimmed it to length setting the headspace with the size die. However, an old timer told me that if I would oil the 7x57 case before I fire formed it, it wouldn't separate at the head. He was right. That was the easiest way to get good cases for the rifle. The simplest thing now though would be to figure out how much excess headspace it has, remove the barrel from the action, Set the barrel up in the lathe and turn the barrel in enough to get the headspace set correctly. I still have that old rifle, never have taken the time to fix it.

  7. #7
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    Quote Originally Posted by jackie schmidt View Post
    What I am reading is when you chamber your formed class, you have .005 headspace between bolt face and the face of the case.

    I personally think you are looking for a problem that doesn't exist. Load the rounds with a good tight neck tension, seat the bullet out so it jams into the lands, put a thin coat of sizing wax an the case and fire them.
    I agree.

    I use the same method for making my Dasher brass, 0.002" neck tension and a 0.030" jam and that blows the shoulder forward around 20x more than the OPs 0.005" perfectly safely.

    Can I ask why you suggest a thin coat of sizing wax, what does that do?

  8. #8
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    Quote Originally Posted by Curious View Post
    I agree.

    I use the same method for making my Dasher brass, 0.002" neck tension and a 0.030" jam and that blows the shoulder forward around 20x more than the OPs 0.005" perfectly safely.

    Can I ask why you suggest a thin coat of sizing wax, what does that do?
    Sometimes with a headspace on the loose side, the firing pin will drive the case forward a little, (even though the bullet is jammed), and the case walls will grip the ask, not allowing the head of the case to seat firmly against the bolt face.

    A little sizing wax insures the case takes the full form of the chamber.

  9. #9
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    Quote Originally Posted by jackie schmidt View Post
    Sometimes with a headspace on the loose side, the firing pin will drive the case forward a little, (even though the bullet is jammed), and the case walls will grip the ask, not allowing the head of the case to seat firmly against the bolt face.

    A little sizing wax insures the case takes the full form of the chamber.
    Interesting, thanks!

  10. #10
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    Quote Originally Posted by jackie schmidt View Post
    Sometimes with a headspace on the loose side, the firing pin will drive the case forward a little, (even though the bullet is jammed), and the case walls will grip the ask, not allowing the head of the case to seat firmly against the bolt face.

    A little sizing wax insures the case takes the full form of the chamber.
    Actually it's "always" not "sometimes".......although the only person other than myself who cares to test it is the late Skip Otto. Skipper and I ran this argument back and forth until I goaded him into testing it, whereon he proved that it's completely impossible to "hold the case back" using jammed bullets. RIP Skip, you were a beaut.

    As per the case gripping the sidewalls, this is also "always"......it will NEVER come back to the boltface on it's own with a proper load...... unless the case is greased. Something which I violently and vehemently disagree with.

    Again, because I've actually tested it.

    But it does make shootable "winning" cases.

    BTW, if it's still in the archives Skip used to also turn his caseheads perfectly flat and concentric to the centerline of his chambers.....until he learnt how to fireform properly.

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