neck trimming,tension,concentric,will it help?

Discussion in 'Reloading' started by bsb, Nov 26, 2007.

  1. bsb

    bsb Well-Known Member

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    Right now I shoot a 7mm sendero(350 shots thru it) and I get consistant
    4"- 5" 5 shot groups at 670yrds
    I also just picked up a 7mm 700P and it shoots the same as the sendero
    (60 shots thru it)
    Question is! if a guy does the neck trimming, tention thing and gets the bullet coming out of the cases straight, realistic what would the group size go down to?
    right now I use the RCBS standard dies and I just reload! No case prep other than chamfer and bevel necks! I am thinking about going crazy on the redding dies, gauges etc
    Thanks for your advice,comments, and those that have been there done that! who might would maybe save me a lot of time and money!
     
  2. AJ Peacock

    AJ Peacock Well-Known Member

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    With factory chambers, neck trimming won't buy you too much if you have good brass. I typically only trim .001" or less off the high side of a lot of brass and call it good. Making the brass thinner means it will be working more each time you shoot and resize it (shorter brass life). If the brass is not consistent, then it will start to bend a little each time it is fired/cooled. I use the concentricity gauge on my fired rounds and toss the ones that are starting to bend (turn into a banana) by more than .001" (I mark them and use them as foulers etc.). The bending is from one side of the brass being thicker than the other side (so it stretches/rebounds differently). Turning the necks to consistent thickness, only fixes the necks. The body of the case usually mimics the inconsistency.

    4-5" repeatable groups at nearly 700yds is pretty darn good, how much better do you want to be? Shrinking the groups by 1/2 would be a lot!

    AJ
     

  3. CatShooter

    CatShooter Well-Known Member

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    What AJ said.

    Turning will get you nothing that is measurable with a factory chamber and factory barrel.

    You would be better off (and save a lot of money and time) if you just buy a fair amount of extra brass, and mic the necks, and throw away the ones that are way out... more than a total of 0.002"
     
  4. bsb

    bsb Well-Known Member

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    Thanks for the info! that does help a lot! the groups are pretty good and I thought if it would cut the group size in half I would do it, but it dont sound like it will do much with the factory chambers, and it makes sense what you guys said.
     
  5. Chawlston

    Chawlston Guest

    For me, it is basically a better use of my time to turn the brass case necks initially than to measure the neck thickness deviation/departure with a micrometer or dial-indicating spinner and still have cases that will have different neck tension from one loaded round to another. Once they are the same thickness and concentric (ie., fireformed), one could look elsewhere for additional accuracy "tweaks". And, until you do it, it will always be out there for you to try. Try five or so and see what happens. You may or may not benefit from it. But, you will only find out if you try a small sample.

    Chawlston
     
  6. Winchester 69

    Winchester 69 Well-Known Member

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    Get a run-out gauge and see for yourself how good your loads are.
     
    Last edited: Nov 29, 2007
  7. Nomad

    Nomad Banned

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    Might want to think about true primer pockets and do a flashhole job
    on the inside as well. With standard dies when setting the bullet reseat
    at 90 or so degrees to true.
    Sizing the brass to the chamber if possible on your dies will help a lot also
    to help. Read a book or two on benchrest reloading..
    All the above is good information on the other posts..
     
  8. Ballistic64

    Ballistic64 Well-Known Member

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    If you do get your groups cut in half,come up for the VHA's 600 IBS factory class in Pierre,you'll clean thier clocks.Hell,even if you dont cut them in half,you'll make a good run of it.
     
  9. overbore

    overbore Well-Known Member

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    Loaded round runout

    is the critical item for factory chamber.. See my post for exact specifications. Overbore
     
  10. wnroscoe

    wnroscoe Active Member

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    All Good Points But

    Conceder this. With the necks turned to a uniform diameter you get uniform neck tension and with the use of a FL Bushing Die without an expander ball Case Neck Run out is greatly minimized if not completely eliminated. I tested numerous fired cases in Factory and Custom Rifles. FL Dies with bushings and standard FL Dies were used. I found that it is in the sizing portion of the process where Run out is introduced into the case and, it is when the neck is being sized that this occurs.

    Two things reduced or eliminated the run out, one was not sizing the neck more than .005" at a time and the other was not using the expander ball, I know, no expander ball is a no brainier. Cases sized with the bushing die when the bushing was removed had .000" run out in the neck. When the bushing was re-introduced and sizing in the neck was more than .005", at least .002" to .003" run out was present.

    I think the best way to remove as much run out as possible is to turn the necks for a 100% clean up only, use a FL Bushing Die with no expander and not size the neck more than .005" at a time, this means using two or more bushings in the sizing process.

    As a result, the .308 Factory Rifles tested were shooting groups in the mid to high .2's at 100 yards and the others were shooting consistent groups under .5MOA to 330 yards. One such rifle has accounted for 1-600 yard kill, two 550 yard kills and countless 400+ yard kills. It's a Remington 700 in 7mmRM. This has been our finding and is worth the effort IMHO, as always, YMMV
    .
     
  11. Winchester 69

    Winchester 69 Well-Known Member

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    Very beneficial input. I have some questions for completeness of the analysis:
    1. Was the sizing stem straightened?
    2. Was the expander ball polished?
    3. Was the expander ball or sizing stem free-floated?

    Glen Zediker has a philosophy that suggests not turning more than 50% of the neck circumference, primarily to prevent overly thinning of the brass that promotes excessive expansion in the chamber. Do you have any countering perspective that you could offer?

    Thanks very much for sharing your experience. I agree with your approach.
     
  12. wnroscoe

    wnroscoe Active Member

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    Very beneficial input. I have some questions for completeness of the analysis:

    1. Was the sizing stem straightened?
    No. Factory stem, nomds.

    2. Was the expander ball polished?
    I've tried polishing the expander ball in the past and yes, it helped. I feel that a carbide ball would be best though, if one was so inclined to use it.

    3. Was the expander ball or sizing stem free-floated?
    No. I set the stem in line with the flash hole and locked it down.

    When I started turning my necks at first, I would turn about 70%. I now turn 100%, just to clean up fully.

    I just finished a 6mmXC project, full custom. It has a .273" no turn neck and will be a Tact/Comp Gun. We'll see how it shoots.

    As far as a "countering perspective", thinning case necks does coincide with having to size the necks more than .005" which I feel is unavoidable with factory chambers. You just have to learn to deal with what you have and what it takes to make it shoot. There is a Tractor Trailer load of factory rifles out there that will flat out shoot. The problem is their owners dont know how to make them shoot, thats the difference between the readers here and them. The readers here are getting it done.
     
    Last edited: Dec 2, 2007
  13. Winchester 69

    Winchester 69 Well-Known Member

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    Thank you for the further input. I have settled on the FL bushing approach, but am still evaluating neck turning before experimenting there.