Concentricity Question

Discussion in 'Long Range Hunting & Shooting' started by Deputy819, Feb 6, 2018.

  1. Deputy819

    Deputy819 Well-Known Member

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    Hey All! Was reading an article by a guy who was comparing a shooting session between 6mm Creedmoor and 6.5 Creedmoor the other day and one of the things he said he did during the comparison was to check the Concentricity of his handloads on a Hornady Concentricity Gauge, mark the "High Side" of a loaded cartridge and then shoot that marked cartridge after loading it into the chamber in the "Twelve O' Clock" position. Anybody here doing that? I'm currently working on loads for a custom 6mm Remington that just doesn't seem to want to repeat really great groups and I was wondering if doing the above procedure might help. Thanks.
     
  2. highdrum

    highdrum Well-Known Member

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    You try to remove any concentricy issues with hand loading. If you're getting a consistent high side on you run out, you should stroke your seating die half way, rotate the case 180° then repeat full stroke of your seating die, may eliminate the high side.
     
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  3. Joefrazell

    Joefrazell Well-Known Member

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    I've done it with no effect on accuracy that I could tell. I stopped
     
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  4. Barrelnut

    Barrelnut Well-Known Member

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    Have read stories of military competitors using that method when they had to use their military issue ammo for the match. They would roll the ammo on the table to find the high spot and mark it. Never tried it myself, but it might work, but would depend on how much the ammo varied and the degree of that variance.

    If you suspect a concentric "runout" ammo issue, it would be a good idea to identify the cause of the runout and fix it. A lot of times runout is caused by the dies themselves.
    * If you are using long pointed bullets like Berger VLDs, the seating stem may not rest on the bullet tip correctly and seat the bullet crooked.
    * Dies that just "neck size" can cause the neck to be off-center from the case body.
    * Full length sizing dies can pull the neck off-center with the expander ball.
    * The length of the arm holding the expander ball can get to be an issue.
    The list of things that can cause it goes on and on...

    The Hornady Concentricity gauge will show that there is a problem, but not necessarily which step in the process this causing it. To find what, you need a gauge that can measure the case itself. Link below is to a gauge that is able to do that. You can measure the case body runout, the neck runout in relation to the case, and finally the runout with a seated bullet.
    https://www.brownells.com/reloading...y&utm_campaign=itwine&utm_content=749-007-305
     
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  5. Deputy819

    Deputy819 Well-Known Member

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    Thanks for the replies, guys! I weigh and sort my brass (Hornady) and I'm currently using Lee Collet Dies for neck sizing and a Redding body die only when my brass feels difficult to chamber. Have been rotating half way through the sizing process, too. My 6mm Remy has a standard SAAMI spec chamber that was cut with a brand new Manson reamer and I've discovered 2 definite dislikes of this rifle (after wasting 50 pcs of brass). One--- This rifle doesn't even like to have ONLY the high side of the neck turned. Really messed with accuracy that I can tell this rifle wants to show me. Two----even with a 1-9 twist Douglas barrel it doesn't seem to like "long for caliber bullets" so I've settled on Sierra......for now. I've ordered a Forster Concentricity Gauge to see what it can tell me about my loads. Thanks again fellas!!
     
  6. Garycrow

    Garycrow Well-Known Member

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    Instead of marking the high side a better practice is to get it to where it's as close to zero runout as you can get, that way you don't have a high side. I've found that the straighter my ammo is the better it shoots.
     
  7. RockyMtnMT

    RockyMtnMT Official LRH Sponsor

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    The better put together the rifle the less the concentricity of the ammo matters.

    Steve
     
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  8. Deputy819

    Deputy819 Well-Known Member

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    @RockyMtnMT
    The Gunsmith that built this rifle for me has been in the business 40+ years and built his own benchrest rifles when he was competitive. I've asked him about this rifle and it's tendency to be "inconsistent" and his response was for me to load some ammo and let him shoot some groups with it. Will he see something different than what I'm seeing on paper? Concentricity issues maybe? I don't know. While I don't have 40+ years experience in handloading I have managed to get my SD's and ES's into the single digits on a fairly regular basis, but so far I've been unable to find any accurate handload combinations for this rifle that will repeat. Could it be the rifle?
     
  9. Barrelnut

    Barrelnut Well-Known Member

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    Interesting problem you are having. Yes, it could be the rifle. And yes, it might not be the rifle....

    What type rifle is this? Hunting/target? 1K benchrest? Weight, etc? What types of groups is it shooting? What are the inconsistent groups like?

    One thing for sure, having the guy who build it shoot it, should be a real eye opener. He sounds like a good smith. I would take him up on the offer.
     
  10. ShtrRdy

    ShtrRdy Well-Known Member

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    What sort of inconsistancy are you seeing?
     
  11. RockyMtnMT

    RockyMtnMT Official LRH Sponsor

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    I would take him up on it. Anytime I can get someone with better/more experience to help with a problem that is a great thing.

    Sounds to me like your loads are good.

    Steve
     
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  12. MagnumManiac

    MagnumManiac Well-Known Member

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    In a distant lifetime when I was very anal with my comp loads, using mandrels in .0005” increments and turning necks to within .0005” of each other trying to get ever increasing minimal runout. I twigged that perhaps I was wasting my time.
    I ran a test with everything the same except the amount of runout. 11 rounds of each fired in the exact same conditions, same day and barrel cleaned of carbon before each string, which I shot just as I would during a match. They went .001” runout, .003”, .005” & .008”. 10 rounds fired with the 11th round chambered and removed & carefully stored as to not induce any bullet movement. Which they were later retested and found that except for the .001” runout cartridge, all the others had changed by at least .002” and the .008” set had gone back to .003” just form chambering them. All loads were just kissing the rifling, not jammed by any means.
    I could NOT decipher any discernible difference between the 4 groups, normal deviation of velocity could have influenced any one of those groups to look how they did. All groups were within my normal outcomes @ 600mtr and what I expect from that barrel. There wasn’t a single flier amongst the 4 groups and they measured within 1/16MoA of each other.
    I repeated the same test in my 6.5x47, it had the same results, it just didn’t influence the end result in any measurable way.
    I have seen greater shift in groups from vertical influenced by velocity swings than I could see from these 2 tests.
    All loads used were highly tuned which I feel is more important than a bit of eccentricity in bullet alignment.
    With partial sizing, the case is free to self align with the bore and chamber, which I feel compensates for slight eccentric problems.
    My 222 has a fair amount of runout, it still shoots tiny little groups with tuned loads.

    Go figure.

    Cheers.
    :)
     
  13. Deputy819

    Deputy819 Well-Known Member

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    @Barrelnut & ShtrRdy
    This rifle is a Hunting/Target Rifle and pretty heavy. Stainless steel Douglas XX air-gauged barrel 1" in diameter at the muzzle. Holland recoil lug, blueprinted Rem 700 action, Jewel trigger (currently set at 1 lbs) and all skim bedded into a Choate tactical stock. My "Avatar" for this Forum is actually a 200 yard target I shot with this rifle a few months ago and that particular group was less than an inch. Funny thing was the next day I loaded that same recipe up and it turned into a 4" group. Same components, same COAL, same everything. I'm still scratching my head on that one. This rifle is funny in that it is very consistently INCONSISTENT.
     
  14. Deputy819

    Deputy819 Well-Known Member

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    20180118_123408.jpg
     
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