Vertical Dispersion

Discussion in 'The Basics, Starting Out' started by Tim Behle, Aug 16, 2003.

  1. Tim Behle

    Tim Behle Well-Known Member

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    I hate to ask some of you to keep repeating yourselves. But the old posts I've been looking for seem to have disappeared.

    I've been working on some loads in the 300 Tomahawk at both 300 and 800 yards. I worked with Retumbo the last few weeks, and am just starting to work with H1000. I'm trying hard to get good measured powder, but it doesn't seem to matter. Even when I dump my loads, I get a lot of vertical in my groups. I've had several groups at 300 that could nearly be hidden under a popsicle stick.

    What are the major causes of this? Inconsistency in the bullets? Inconsistencies in how I hold the rifle?

    Any help you could give would be greatly appreciated.

    Tim

    [ 08-16-2003: Message edited by: Tim Behle ]
     
  2. BountyHunter

    BountyHunter Writers Guild

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    Tim

    You said "measured powder". Almost impossible to use a powder measure to dump charges for the big cartridges. got to weigh each one!

    That could be first problem. Then tail or head wind, clouds coming and going causing your aim point to move optically up and down. Do not shoot free recoil also, hang onto the gun.

    Most frequently you need to come up or down a little on the powder as the primary cause of dispersion. Have you tried the ladder method at about 300-400 yards in a no wind condition to find the barrels sweets spots with that bullet, primer and powder combo, if not go into bullets ballistics and think the date is 12-24-02 for explanation.

    BH
     
  3. 308 Hawg

    308 Hawg Well-Known Member

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    I would suspect a wide extreme spread on velocity or too soft bags as things that might be causing the vertical.
     
  4. westbronco

    westbronco New Member

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    I've always heard that vertical strings are caused by over gripping with the left hand (right handed shooter) and horizontal stringing is caused by the right hand. That has seemed to hold true in my shooting, but would like to hear other opinions.
     
  5. Tim Behle

    Tim Behle Well-Known Member

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    Sorry, poor choice of words on my part. I did mean to say that I was very careful to make sure each weighed exactly the same as the one before. But at this point, I'm not sure that helps. A week or so back, I wanted to test the consistency of my electronic. So I broke out the old Lee beam scale. Loaded five rounds off of it, five rounds off of the RCBS, then just for the heck of it, I dumped five more. Both weighed charges gave me 8" groups at 800 yards. The dumped load gave me a 6" group. I thought it was a fluke, and tried it again a couple of hours later. The wind picked up, one group was just over 10", the next just under 10" and the dumped load shot 8".

    How tight should the bags be? I use the Sinclair adjustable front rest, and keep it snug to the sides of the stock. My left hand squeezes the Protector rear bag. It never touches the rifle. I've tried the ladder method with different powders, if this rifle has a sweet spot, it's hard to determine. It shoots good, but not good enough to make me competitive.

    What would you consider the best distance to test loads?
     
  6. 308 Hawg

    308 Hawg Well-Known Member

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    Are you shooting free recoil or do you have your shoulder against the stock? Firmly against the stock or really snug against the stock? Some calibers dictate how you have to hold them, some allow you to be less controlling.
    I like to shoot 5 shot groups at 200 yards. If less than 1/2" group and less than 15 f.p.s. extreme spread it usually will be competitive at 1000 yards. This is for 16.5# 6 and 6.5 cal. guns and .30 cal. 75# rifles, not for boomers that you hunt with.
     
  7. STL_Shooter

    STL_Shooter Well-Known Member

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    I must use extremely firm shoulder pressure straight back into my shoulder. Any thing less delivers acceptable results in my 6mm or .223 but stinks with the mighty Wolf.

    Bottom line - I think that kind of vertical dispersion either means something loose on the rifle (unlikely, would also cause horizontal dispersion), or (much more likely) too light or inconsistent shoulder pressure...
     
  8. Brent

    Brent Well-Known Member

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    Tim,

    I'm sure it's already freefloated, but my dads 300 WSM was vertically stringing, from horrible, to just noticably unacceptable, but almost with every group. We finally took the strain gage hook up cord off the rifle, as it was the only thing touching the barrel, and we couldn't find a single other problem... Well it worked beautifull after that, plain and simple, nice small round groups, group after group, after group... What a freaking difference!! All the load development I've done with my rifles with them cords just touching, to being sligtly pinched in between the stock and barrel is kind of making me sick the more I think about it... Been changing the way I do it now tho. Ain't shooting groups with the cords on no more, just have to give up the pressure data during them tests and get it all before hand.