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Why am I getting vertical strings in my grouping?

Discussion in 'Competition Shooting' started by Ruger 15151, Apr 3, 2017.

  1. Ruger 15151

    Ruger 15151 Member

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    Today I was doing some load development for my 9mm Glock (Storm Lake Barrel) and 9mm M&P CORE (Storm Lake Barrel). Both groupings where shot with 5.2gr (Glock) and 5.4gr (M&P) of BE-86 behind an Extreme 124gr RN . I was using a pistol rest and distance was 15 yards. I have a Trijicon RED dot on both so sight picture issues should be eliminated.

    Also, I shot at least 2-3 groups with 5 different loads for each pistol so my technique shouldn't be the issue. I have read that M&P 9mm's sometimes unlock early. However, I got a similar string with the Glock as well. I know BE-86 works great in 9mms because I get 7/8" groups with the Glock at 15 yards with a 115gr ZERO FMJ-HP behind 5.2 gr of BE-86.

    What is causing these strings from both pistols?
     

    Attached Files:

    Last edited: Apr 4, 2017
  2. Jim Watson

    Jim Watson Member

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    What kind of rest? It is possible to get bounce off sandbags.
     
  3. JohnKSa

    JohnKSa Member

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    That was my thought too, as soon as I saw you were shooting off a rest. If you're resting the gun on a hard rest, put a pad in between the rest and the gun. Better yet, rest your hands and perhaps the butt of the gun on something relatively soft, but keep the rest of the gun from touching anything.
     
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  4. Ruger 15151

    Ruger 15151 Member

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    I'm using this rest:

    http://www.ctkprecision.com/compact-shooting-rest.aspx

    it has thick padding.

    I would normally agree with with Jim and JohnSa that the pistol is bouncing. However, these were the only 2 out of 17 groups with vertical strings. I shot under 1" groups with the same pistols on the same day using the same rest. That's why these 2 groups are so perplexing? Why are they in almost a perfect vertical line with no windage variation. without the elevation difference, these 2 groupings would likely be one ragged hole. Unfortunate, neither the M&P nor Glock are capable of that type of accuracy.
     
  5. macgrumpy

    macgrumpy Member

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    Is that an 8 MOA red dot?
     
  6. ATLDave

    ATLDave Member

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    The simplest explanation would be that you shot 17 groups. Simple random variation/deviation will eventually cause some shot arrangements that our brains, which are hard-wired to look for patterns, interpret as meaning something.
     
  7. Jim Watson

    Jim Watson Member

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    That was not clear to start with.
    The answer is random distribution. As Bart B. points out to rifle shooters, every group is different.
     
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  8. Ruger 15151

    Ruger 15151 Member

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    Here is a great article in in 6mmbr that discuss reasons/cure for vertical and horizontal strings.

    http://www.6mmbr.com/verticaltips.html

    They aren't always random groupings. Unfortunalty, most of the issues mentioned don't apply to pistols.
     
  9. Ruger 15151

    Ruger 15151 Member

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    I have a 3 MOA on the M&P and 6 MOA on the Glock. I usually turn the brightness as low as possible and still see the dot. I use a orange dot on the target to help center the red dot.
     
  10. ATLDave

    ATLDave Member

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    If every group you shot had this pattern, you would have a vertical stringing issue. If half did, you might. Two of 17 groups did. What factor was present for those two groups and not the others? If you can identify that thing, then that was the cause. If nothing was different, then randomness is the fairly obvious explanation.

    If you flip a coin 5 times and record the results, and then do that 5-flip-group 17 times, the odds are strong that one or more of those groups will come up all heads or all tails. Doesn't mean the coin is broken.
     
  11. Ruger 15151

    Ruger 15151 Member

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    I hear what you are saying. Its difficult to shoot 5 different groups with the same load and get the same pattern more than twice on some days. However, what confuses me is that these 2 groups out of different guns but with similar loads (5.4gr & 5.2gr of BE-86) with the same bullet ( Extreme 124gr RN .3556 ) produced almost perfectly vertical strings.
     
  12. ATLDave

    ATLDave Member

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    Did you shoot other groups with those same exact loads?
     
  13. Ruger 15151

    Ruger 15151 Member

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    I only had enough rounds at 5.2gr to shoot a second group with the Glock. I saw very similar results but the vertical string was a little more varied. ( 1 shot was pulled low )
     

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  14. Hoser

    Hoser Moderator

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    Varying grip pressure.

    Thats why Ransom rests are so good, they take the human element out of it.
     
  15. Ruger 15151

    Ruger 15151 Member

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    That makes sense.

    The pistol rest that I am using has a V-block to support the barrel/frame and an adjustable pad to support the bottom of the grip. I can't get a normal grip with my weak hand and still rest the bottom of the grip on the pad. Therefore, I have adjusted my grip slightly because I thought resting the bottom of the grip on the pad would eliminate any elevation movement.

    However, I have made more rounds using the same load data. This time, I will use my normal grip and grip pressure and make sure the bottom of my hands are resting on the support pad instead of adjusting everything so the bottom of the grip rests on the support pad.

    Minus the elevation variations, both these would produce some pretty tight groups.

    I'll share my results once I am able to get to the range.
     
  16. Ruger 15151

    Ruger 15151 Member

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    Thanks everyone for your input.
     
  17. lonegunman

    lonegunman Member

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    Control your breathing. Check your grip and make sure it is the exact same every time and your sight alignment might be varying if you are looking over the top of the gun to try and see the bullet holes.
     
  18. J-Bar

    J-Bar Member

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    I'm curious, did the stringing occur in a "marching" sequence, with successive shots always impacting higher than the previous shot, or did the impacts simply fall into the same vertical line with no other pattern? I'm not sure I have a good explanation either way, but if there is a pattern to the change in the point of impact from shot to shot, it could help provide an answer.
     
  19. dieselchief

    dieselchief Member

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    hate to admit it but I shoot vertical groups also. it is my eyes messing with me as my blood sugar varies. type II with metforum pill morning and evening. gracious health warning sign.
     
  20. tuj

    tuj Member

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    think about it, the common factor was that you loaded the ammo. Also common, the powder, and the bullet type. Usually from a rest, vertical stringing is caused by subtle variations in velocity. This means that either your powder metering is not accurate enough, or your powder charge is not being completely or consistency burned, which might point to primer issues. I'm not trying to say you don't know how to load, far from it. I'm merely pointing out what I've noticed in match and quality hand-loads, versus factory range ammo.
     

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