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Thread: help diagnose an accuracy problem!

  1. #1

    help diagnose an accuracy problem!

    Sako 75, in .243, with a factory wood stock, not bedded. 22" barrel, not screw cut. Optilock rings and mounts (2 years old). Meopta 3-12X50 scope. Shooting Hornady Superformance 95gr SSTs.

    When initially set up with this combination (about 18 months ago), the rifle shot extremely well indeed (touching holes at 100m, if I was on form).

    Last autumn, I started to get a series of unexplainesd misses or really poor shot placement. First inclination was to blame myself. But I was still shooting fine with other rifles. So started to test it periodically.

    First 2-3 shots of a session would still group very well, often overlapping holes. However, the POI of these holes shifted unpredictably between sessions, by about 1-2 inches. Initially, I made the mistake of firing one round, adjusting the scope, firing two more to confirm, and going home happy without further testing.

    However, after this happened 3-4 times, I got suspicious and started firing longer strings. Again: first 2-3 shots on top of eachother, and then they'd start to wander. No consistent pattern to the wandering: the group just started to dramatically open up, to about 3 inches.

    I've checked scope mounts - all tight. Scope itself tracks fine.

    I'd be EXTREMELY grateful for suggestions!!

  2. #2
    I've had similar experiences with the same rifle until it was pointed out to me that it was possible to move the barrel & action from it's relationship to the stock by pushing the barrel one way & the stock fore-end in the opposing direction. The implication of this was that everything could move about between shots & I had struggled for a long time to get the rifle to shoot predictably after zeroing. Bedding & maintaining a consistent cleaning regime seems to have sorted it out for me.

  3. #3
    It sounds like the action is moving in the stock on firing, ---either loose bedding screws or bedding problems?? -- Maybe a good time to pillar & glass bed the beast.


    p.s. Is there any muck jammed under the barrel affecting the free floating clearance?
    Last edited by Yorric; 25-03-2016 at 10:19.

  4. #4
    Have you checked your stock bolts?

    I noticed that the stock bolts on my 85 had shot loose the other day yet amazingly the rifle was still shooting 1" groups. Tightened them up and back to half inch or less. It's a varmint model a sporter weight would probably have shown up the problem more I think.
    Last edited by 8x57; 25-03-2016 at 10:27.
    It's the calibre of the shooter that counts not the calibre of the rifle.

  5. #5
    It's almost certainly a function of barrel warming and then warping. My Heym does this. It is almost impossible to have the bore absolutely concentric with the outside of the barrel. Barrel wall thickness will vary. As it warms up metal expands and the different thickness will mean it will expand by different amounts thus warping the barrel. All barrels do this, but with a heavy weight target barrel the thickness of the barrel walls means less % change from one side to the other. But a target barrel needs to shoot long shot strings.

    in a sporting rifle there is a compromise between weight and repeatability. What matters is first round accuracy out of a cold barrel.

    The other thing that will have a big effect is your technique and consistency of technique and hold and management of recoil. A firm grip is more consistent.

    And dont overthink it. We are all obsessed by tiny little groups. What is needed is can you put a bullet through heart and lungs at respectable ranges.

  6. #6
    Have you considered cleaning the barrel and I mean right back to bare steel and then retesting?

  7. #7
    I have a Tikka 595 in .243 and had a problem where first shot or two was bang on then next couple went random, maybe 4 inches away from the first. To cut a long story short it turned out the cause was barrel throat erosion. Hope your problem is different and easier to fix, but might be worth checking if you know someone with a bore scope. A friend looked at mine from the muzzle and it looked fine, looked from the other end and it looked like charred timber with deep copper veins running through it.

  8. #8
    Following on from my previous post. It doesn't take much heat to expand metal. Guy Martins Spitfire - go to 4od and you should find it - shows fine machining of the pins that hold on the wings. Ground to very fine tolerances and fit perfectly when cold. Guy Martin does a piece to camera holding one of the pins. The warmth from his hands is enough to expand then pin by one or two thou so that it won't fit.

    Go go back to a sporting rifle barrel. A shot string of a few rounds warms the barrel. If it feels warm it up will be well above body temp of 37 degrees C. That could well warp the barrel my several thou at the muzzle. - and one thou effect at the muzzle is 200 thou effect at 100 yards (assume barrel is 18 inches).

    Some modern double rifles have screw adjusters on the barrels to set the convergence. 1/4 turn on a screw can move point of impact two or three inches.

    i had exactly this problem when I first got my 243. The chap in the gunshop told me take to take a thermos of tea to the range. Shoot one bullet, open the bolt, let barrel cool whilst having a cup of tea, and then shoot another.

  9. #9
    Same happened to me. Tightened them up and back to normal.

  10. #10
    Assuming crown and barrel etc are tip top I'd say it's eigher moving in the stock or have you checked the free float between barrel and action or take the action out the stock and check there is nothing lodged between barrel and stock etc

    if if you can try another stock that's tight to the action it's worth s try

    pillered and bedded or even just pillered will make a huge difference

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