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Thread: consistent odd grouping

  1. #1

    consistent odd grouping

    I have an ongoing accuracy problem with a Sako 75 in .243, and would be very grateful for input.

    After a previous consultation on here, I got the rifle glass and pillar bedded by a respected smith.

    It now behaves extremely predictably:

    First shot from a cold barrel is dead on. First shots from successive groups fired 5 mins apart overlap. In fact, if i just took the first shot from each group, they form a single ragged hole.

    Second shot from a group goes 3 inches right and an inch and a half up. Again, very consistent - forms a respectable group of its own.

    Third shot from a group ends up roughly in between first and second, but with less consistency.

    So: what's happening and what can I do?

  2. #2
    Quote Originally Posted by Mungo View Post
    I have an ongoing accuracy problem with a Sako 75 in .243, and would be very grateful for input.

    After a previous consultation on here, I got the rifle glass and pillar bedded by a respected smith.

    It now behaves extremely predictably:

    First shot from a cold barrel is dead on. First shots from successive groups fired 5 mins apart overlap. In fact, if i just took the first shot from each group, they form a single ragged hole.

    Second shot from a group goes 3 inches right and an inch and a half up. Again, very consistent - forms a respectable group of its own.

    Third shot from a group ends up roughly in between first and second, but with less consistency.

    So: what's happening and what can I do?
    I used to get that from Ruger factory barrels from the 1970's. No bedding, cleaning, prayers or bribery would make the 2nd and third shot go to their older brother. I finally came to the conclusion that the barrels just weren't good. I rebarreled all of them.~Muir

  3. #3
    Have you tried different ammunition (assuming factory) or tried a different bullet or played with seating depth if reloading, or as Muir suggests it might be the barrel, although the Sako's are usually good. Does the smith who bedded it have a bore scope? Always worth getting someone else to shoot it as well just to rule out shooter error

  4. #4
    Quote Originally Posted by Akeld View Post
    Have you tried different ammunition (assuming factory) or tried a different bullet or played with seating depth if reloading, or as Muir suggests it might be the barrel, although the Sako's are usually good. Does the smith who bedded it have a bore scope? Always worth getting someone else to shoot it as well just to rule out shooter error
    I haven't tried different ammo, but given the consistency with which this happens, I don't think the ammo is the problem. With an ammo issue, wouldn't you just expect a big group, but without the very regular pattern within a shot sequence?

    I don't think it is shooter error, becuase: (i) the consistency; and (ii) I was alternating between the .243 and a .270, and was shooting my .270 perfectly well (I imagine it's pretty unusual to be getting better grouping from an unmoderated .270 than from a moderated .243!). Shooter error is my default explanation for any problems, and I think I can rule it out here.

  5. #5
    Could it be moving ever so slightly in the bedded stock thus given you a double group! I think they call it double pinching on the action,

  6. #6
    I refer to my standard caveat regards rifle barrels - 9/10 witchcraft!

    I have come across this with various rifles across several makes. I have a suspicion - but must be honest that's all it is. The most worrying instance was decades ago with a certain major urban police force. At the time they had 22-250 & 243 Parker Hale 1200's as their sniper rifle. I noted a 'range card' on the stock of each and thought a good idea - until I read it! It went along the lines of 1st shot 'on', 2nd within 20 seconds 3" low/5" left, 3rd shot - and so on. Pity the second hostage in the 'queue'!

    The worst offender was a 7mm-08 A bolt that pulled off some atounding results for me, but honestly - you never really knew what it was going to do next.

    From the symptoms you describe I think the issue lies with the barrel. Its a matter argued to the point of Fatwa on here - so I'll re-iterate its just my best guess, I'm really not interested in duelling over it

    Machining/ manipulating a barrel induces stress. The exact nature of that stress is hard to predict - but heat treatment is fairly advanced as a science and often deployed to relieve stress as much as achieve a given temper etc. Heat causes a reaction in metal - it wants to move. Forces of expansion/ contraction are massive. I have seen a barrel exhibit similiar symptoms - having been previously 'fine' - close examination showed a ding in the metal about 6 inches ahead of the chamber - not sure what that proves or otherwise, but it wandered shots as the barrel warmed thereafter.

    Mike Norris penned a post on a thread about barrel break in ( another Fatwa inducing topic ) and from recollection relayed advice relating to similar behavious from barrels not conditioned and the inflammatory view ( relayed by him from another ) that often once the conditioning process was bypassed, a barrel may never fully respond. I'm not suggesting a break-in/ comditioning issue here. Just as example.

    I think Craig Boddington referred to similiar symptoms - but dont recall where - which were alleviated to some extent by Cryo treatment on the barrel.

    None of that provides a solution I'm afraid, just a possible root. It could be that the bedding has merely settled the pattern into something more predictable?
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  7. #7
    Sigh - I'm increasingly afraid you might be right, Andy.

    I think the one thing I can firmly conclude from this whole sorry experience is that I should never have sold my T3, which shot beautiful groups with every ammo I gave it.
    Last edited by Mungo; 21-04-2016 at 08:44.

  8. #8
    It sounds like something is moving despite the beddign job and I will bet that the barrel is free floated too.

    I am going to suggest that yon dampen the barrel. Get a glazed business card and cut into strips and place under the barrel about 1" back from the front of the stock so that there is upwards pressure on the barrel. Hoping that you do not have a stock with enough gap here to swallow a herd of elephants and try it. pressure needs to be enough to hold barrel in place and dampen the pulses of the firing cylce.

    Not my idea so cannot take the credit as pressure pont beding is as old as the hills and the card trick came from a thred about free floating and how it did not suilt a rifle but pressure point bedding sorted it out.

    http://www.go2gbo.com/forums/bolt-ac...oint-question/

    and one from the archives of this very forum ..

    http://www.thestalkingdirectory.co.u...p/t-85897.html

    Just a suggestion of course and apart from a little time a cut up card and a few rounds what is there to lose?

  9. #9
    crap barrels don't show consistency

    my money is on action/stock interference

    especially if the shot sequence is "walking" in a roughly similar direction

  10. #10
    Quote Originally Posted by Conure View Post
    It sounds like something is moving despite the beddign job and I will bet that the barrel is free floated too.

    I am going to suggest that yon dampen the barrel. Get a glazed business card and cut into strips and place under the barrel about 1" back from the front of the stock so that there is upwards pressure on the barrel. Hoping that you do not have a stock with enough gap here to swallow a herd of elephants and try it. pressure needs to be enough to hold barrel in place and dampen the pulses of the firing cylce.

    Not my idea so cannot take the credit as pressure pont beding is as old as the hills and the card trick came from a thred about free floating and how it did not suilt a rifle but pressure point bedding sorted it out.

    http://www.go2gbo.com/forums/bolt-ac...oint-question/

    and one from the archives of this very forum ..

    http://www.thestalkingdirectory.co.u...p/t-85897.html

    Just a suggestion of course and apart from a little time a cut up card and a few rounds what is there to lose?

    Thanks! I had heard (and thought about) this. I will give it a go.

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