Questions regarding properly sizing belted cases

Discussion in '7mm STW' started by cerwin, Apr 29, 2013.

  1. cerwin

    cerwin Well-Known Member

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    I just purchased my 1st 7 STW. I have laundry list of questions regarding loading for this cartridge. I have some experience loading other beltless cartridges.
    I'll apologize in advance if the answers are here but don't have time to study the forum in detail.

    Belted cartridges are new to me and as I understand are head spaced off the belt, this would present a different set of challenges for me. To my understanding it seems that with belted cartridges head spacing would also need to be on the shoulder as well for best accuracy. With 2 head spacing points does the belt tend to interfere with proper center bore alignment from shoulder head spacing. Do the belted cartridges require less to no shoulder bump to properly align cartridge with bore upon firing.

    My next question is: I have 2 sizer dies for this cartridge. Neither one seems to be able to produce concentric necks. A WAY, I've found to get fairly concentric necks is to rotate 90 degrees part way through, size a little more, rotate 45 degrees, rotate 90, size rest of the way. I've been expanding with Sinclair expander for consistent neck tension. The problem is, my accuracy went away after all the rotations in attempts to get everything strait. Could somebody give me thought on this?

    The rifle is a McWhorter custom, which I've not even fired yet. I've had it for a week now, and can't wait to touch some rounds off. I have load data, and ammo loaded by McWhorter that somehow got destroyed during shipping. Hopefully more will arrive tomorrow.
    I have plenty of all components to load for it, but the concentricity problems have me concerned. I am considering having a custom sizer die built to alleviate the problems I'm seeing with standard production sizer dies, and hopefully prolong case life in the process.
    Any help and suggestions you guy's may have is much appreciated.
     
  2. 7stw

    7stw Well-Known Member

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    Cerwin, I read your thread starter the day you wrote it, but have been busy,so here goes. First of all, congrats on the new rifle. Those " macs" are art forms, and are usually tack drivers in what ever caliber they come in.
    And, of course, Welcome to the Brotherhood!
    As to concentricity issues, for the MOST part, it happens on the resizing stage, and more then probable, when you are on the expander. Better put, when you are pulling down on the case neck. It CAN happen during seating, but is more likely to be in the resizer set up. It can be as little as slightly worn press linkage, play in the die threads, or the shell holder not perfectly square with the ram. Remember, the taller the case, the more deviation is possible. I have driven myself nuts with it before, and finally, I was able to keep it below .002.
    My best explanation is just cross tees, and dot eyes!!! This cartridge is NOT hard to load for. It is very readable, and SHOOTABLE. And I must stress proper initial die set up. That is a integral part of case life, and accuracy as well. Enjoy the ride, and don't be afraid to ask a question or two if needed. This is a " kick ass " round, make no mistake about it! And extremely accurate too!
     

  3. Lefty7mmstw

    Lefty7mmstw Well-Known Member

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    +1 on 7stw's comments.
    I'll toss another thing in too. I hear more peopls having concentricity issues with turrets and progressives than O or C presses. You may want to size with a rather fresh single stage press and lube your necks so the expander doesn't pull the case out of square. Only the bottom half of the case itself really needs lube with this one if you are using a pad and lube; if you lube her all the way up you'll likely get lube dents after the die gets saturated. Just don't get too stingy or you'll stick one.
     
  4. WapitiBob

    WapitiBob Well-Known Member

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    Since all our action truing and reloading is about concentricity and parallelism, I find it odd that nobody takes once fired brass and single point turns the neck ID concentric to the case od.
    Turning the neck od with a neck mandrel gives uniform neck thickness but it's not concentric with the od of the case. You then have to shoot the brass to get the neck od to conform to the chamber and hope the id stays concentric.
     
  5. Greyfox

    Greyfox Well-Known Member

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    Having gone through a few different lots of Norma brass in my 300 WM, if have found it to be very consistent in neck wall thickness running .0145". Great brass, but it should be for the price. With once fired cases I will neck size only for 4 firings, then use a body dye and FL size to .002" shoulder push back. All dyes used are Redding. I have found neck alignment with the case, and bullet run out to be consistently less then .002" by using a Redding S dye, with the busing sized to .002" of neck tension. I will back off the bushing knob on the S dye a small fraction of a turn so you can faintly hear the bushing click due to slight looseness in the dye. This seems to allow the bushing to float and follow the fire formed neck. I'll use a very small amount of Imperial wax on the neck. I have not seen the expander on my specific dye cause alignment issues but I remove it anyway. I will anneal the cases after every 4-5 firings. I have used this approach for several belted case cartridges I have loaded for and it seems to produce very good accuracy, ES and case life. IMHO.
     
  6. cerwin

    cerwin Well-Known Member

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    Thanks for the input guy's. I'll keep a close watch on any variables that can lead to concentricity issues, and eliminate, or minimize.

    I've been loading for 300 RUM for about a year, and have not had the concentricity issues with it, which is the reason I'm wondering if my dies are the problem. I dont use an expander ball (one of the variables I've already eliminated). I'm using a sinclair expander die to keep consistent neck tension, and so far this has not caused any problems. I do have a question though. In an effort to produce perfectly concentric ammo I tried rotating the case numerous times during sizing with a Redding type S neck bushing die. This gave me concentric necks, but the accuracy was not as good as necks that were not rotated, and sized in one step, but not as concentric.
    My question is can rotating TOO much during sizing give inconsistent neck tension, which would lead to decreased accuracy?
    I shot this STW for the first time Tues afternoon, right as a winter storm was blowing in so I didn't shoot much. 2 - 3 shot groups, with ammo from McWhorter. This thing ROCKS! I've never shot a rifle like it before. At 200 yds, 4 of the 6 shots were touching. The other 2 were right there as well but opened up to about 1". This was with virgin never fired brass.
    My thought has been to neck only size for 3 firings, and have custom die made to minimally size cases, and improve concentricity problem. Would that be worth it?
    I have a standard RCBS FL die,, and a Redding competition bushing set. I seem to have problems with both.
     
  7. 7stw

    7stw Well-Known Member

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    Cerwin, Greyfox is dead on , on all his accounts, and his approach is spot on. The other variable, or at ANother variable, is neck thickness, and consistency at that end of the case.
    As for the accuracy you are getting, get used to it. ( especially with that rifle you have). Neck sizing will probably be your best bet for brass life, and accuracy too, but at some point, you will have to give the body a squeeze, and just bump the shoulder back, just a smidge, to keep the chambering reasonably snug, but not TOO snug. Find ing that sweet spot will be your homework. It's a little trial and error game, but the rewards are smoking accuracy, low ES, SD, and DRT deer. Forget federal brass, go with Winchester, or Remington brass, ( in that order, IMHO ), and better yet, fire formed Norma, 300 HH brass. THAT, is the " crem de LE crem" brass set up. That is my next project. That is a smokin set up you have there, feed it right, and it will continue to feed you for a long time!!!:D
     
  8. MR.SWIFT

    MR.SWIFT Well-Known Member

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    not to confuse anybody, i was of the impression that the 7stw case was made from the 8mm mag case necked down. havent payed attention to case length between the 300HH case and the 8mm mag but thought the 8mm was longer. i owned a 7stw for 10yrs or so but always used stw brass.
     
  9. 7stw

    7stw Well-Known Member

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    SWIFT, you are correct on the parent case,( 8 mm Mag). It can however be formed with any of the full length 375 HH based cartridges. Sometimes it may be a single or double stage affair, but with the right brass, it's worth it. With things being the way they are right now, sometimes it just makes sense to " expand your horizons a bit" .
    With Norma brass as the base, the final product will be awesome!
     
  10. cerwin

    cerwin Well-Known Member

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    Greyfox, when using S bushing dies, are you neck sizing in 1 stroke, or do you rotate cases. I've done that and ended up with very concentric necks, but accuracy was a little less than with necks sized in one stroke. Got me to thinking that could be causing inconsistent neck tension.
    I'll back off the bushing knob just a bit as well
     
  11. cerwin

    cerwin Well-Known Member

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    I've heard that and have thought of doing that. I have 0 experience with such case forming. I would.
    Think forming 300 HH brass would be a single step sizing, and then fire forming. Can it be ran through a standard FL die for sizing? Can fire forming be done at moderate loads of different components than I'm using for my real loads?, powder, primer, and bullets.
    Been thinking about trying it. Sounds easy enough
     
  12. Greyfox

    Greyfox Well-Known Member

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    I have never found the need to rotate during the neck sizing process with Redding dyes. If I have had a neck alignment issue I have found the problem to lie else ware. I have tried collet dyes, rotating and not rotating, and while many swear by them, I have found it difficult to get consistent neck tension, and low ES. Just my experience.
     
  13. cerwin

    cerwin Well-Known Member

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    Hmmm, I think maybe your making a good point. Something to think about
     
  14. cerwin

    cerwin Well-Known Member

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    I'm neck sizing only without rotating and they are coming out, for the most part good. Best is .0005, and worse being .003
    Even at that I'm getting some good accuracy. This rifle is a tack driver. I'll post pics of groups