Vertical stringing

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by sambo3006, Sep 15, 2009.

  1. sambo3006

    sambo3006 Well-Known Member

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    I have a 7mm RUM that I pillar bedded into an A2 stock. The bedding job seems pretty neutral with almost no movement when you tighten down the action screws. The barrel is free floated and I don't let it get hot any way. It has a V port muzzle brake from Straight Shot Gunsmithing (308 nate). It has shown a definite tendency towards vertical stringing with 150 gr BT's loaded to magazine length. I haven't chronographed a series of rounds to check my ES yet but at 100 yards groups will be under 0.5" with horizontal spread in the 1's and I shot her at 200 yards the other day. 3 shots into 0.6", again with horizontal spread of around 0.1". All groups shot off sand bags and using a Leupold 6.5-20 SF scope. Ideas?
     
  2. Bull45cal.

    Bull45cal. Well-Known Member

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    So, you are saing that your are getting groups 0.1" wide by 0.5" tall @ 100yrds, and 0.1" wide by 0.6" tall @ 200yrds? Sound pretty good. I don't see how your going to know anything concrete without knowing velocity spread. That's what I would guess, but you won't know for sure until you measure. I was having the same problem (bigger group size though) where the groups looked like a football. I finally broke bad and bought a chrony. Great investment, but I don't know how much help it will be in this situtation, since your talking about a change in velocity that will mostly be within the tolerance of your testing capability (unless your firing from a vise, that is bolted down, and your target doesn't shift "any" on impact). My Chrony at best is within 0.5% accurate. Just something to consider, since that is 15fps @ 3000fps.
     

  3. RT2506

    RT2506 Well-Known Member

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    That is not much of a vertical spread but it could be a number of things. Like has been said it could be velocity spread but you will not know till you check that. It could be that a different primer will clear up that problem. It could be something as simple as your shooting form or hold. Work on only one thing at a time to fix your problem though. One other thought. Have you de-burred the inside flash hole of your cases? This really helped smooth things out in many of my loads years ago when I started doing this.
     
  4. RockZ

    RockZ Well-Known Member

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    It looks like it is shooting well, .6 groups at 200yds!. To really determine the vertical spread you need to get out and shoot at 500-1000yds. Whatever the longest ranges you intend to use the load(hunt) at.
    Then you can really see how the load performs.
    I get an initial load and then do a long range ladder to fine tune.
    There is a good link to the 1000yd ladder test in the reloading forums.
     
  5. sambo3006

    sambo3006 Well-Known Member

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    Not claiming 0.6" average at 200 yds, that was actually the only group fired at 200 yds. She does seem to want to shoot for sure, though. I need to shoot through the chrony next time I'm out there. I have not uniformed the flash holes and haven't tried any different primers. I've been using Fed 215 match primers. If I don't get it figured out before my trip to Colorado for mule deer, I'm not going to sweat it too much. It is still punching some pretty small groups and I'm probably going to limit my shots to 600 yards.
     
  6. Limbic

    Limbic Well-Known Member

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    Sometimes when loads are too hot they can start to string vertically. I shot one the other day with my 260. Four shots all in a straight line. Perfect straight line at 300 yrds. Probably 3-3.5 inches long. MV was too high and the brass had some extractor marks.

    One of the more intersting groups I"ve ever shot.

    Not all of my rifles do this but they ALL act funny with max and over max loads.
     
  7. Bull45cal.

    Bull45cal. Well-Known Member

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    Sambo 3006,

    Read Jerry Teo's load developement article on the home page. It should help you out.
     
  8. elkaholic

    elkaholic Well-Known Member

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    Try checking your case necks for uniformity. Do you outside turn them. Since your talking fairly small groups already, your problem could be as simple as inconsistent neck tension. GOOD LUCK.....Rich
     
  9. Augustus

    Augustus Well-Known Member

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    0.6 in groups at 200 yds and you think you have a problem---- Plaeeeeese!!!!!
     
  10. justgoto

    justgoto Well-Known Member

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    I know! I got a .58 group about a week ago and I am still dancing in the streets! :p
     
  11. Capt Kurt

    Capt Kurt Active Member

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    With groups that tight usually breath control comes into play. Shots must being taken with the chest in the same position each time as chest motion slows on the exhale or vertical stringing can result. To check for this, set your scope on high mag. Get into your shooting position. Follow your crosshairs on your target while your breath in and out. I would venture to say your crosshairs will follow your vertical stringing pattern. Eat a good meal before you shoot and don't drink much coffee. Hope this helps. Capt kurt
     
  12. sambo3006

    sambo3006 Well-Known Member

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    Thanks for the tips, guys.
    I know, I know, why am I complaining about a 0.6" group at 200 yds! Definitely not complaining, pretty danged proud of it if I say so myself. This rifle just shows so much promise to be an absolute hummer that I want to see what the full potential is.
    Definitely food for thought on the breath control. Don't know if that is the case as most of my rifles that are very accurate tend towards the typical cloverleaf group but I will pay closer attention next time at the range. It sure is fun to tune a very accurate rifle instead of trying to find a load that will just get you under 1 MOA!