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Thread: help diagnosing accuracy problem

  1. #1

    help diagnosing accuracy problem

    I'd be grateful for help diagnosing a niggling accuracy problem:

    I have a recently acquired .308, with a 6X42 scope in swing off mounts. For the purposes of this, it was being shot off a bipod.

    After trialling a few different factory loads, I decided on Norma 150gr ballistic tips. These consistently produced goups under an inch at 100 yards at the first range session.

    Yesterday I did some more range work, and was unable to replicate this, ending up with an average group of around 2.5 inches.

    However, there was a distinct pattern to the shots: the first in each subsequent group of three went almost through the same hole (ie. if I were to only take those shots, there would be a very nice group indeed). The second went about half an inch high and a touch to the left, but with more variability, and the third about an inch and a half high with a lot of variability.

    Since I zero using a new post it note stuck on top of the last after each group, at the end of the session, I can peel them all away and look at the aggregate group on the cardboard underneath. This showed 3 distinct groups for each shot.

    Nothing had changed with the rifle in between the two sessions, and it had not received any knocks - I am confident that there is nothing wrong with the set up.

    So my question is this: is such a pattern likely to be the product of something shifting as the barrel heats up with each successive shot in a group? Or can it be explained by my tendency to develop a flinch?

    I am inclined to go with the latter, since I had been shooting clays the day before, and had quite a nice tender bruise on my shoulder. If it is the latter, is such a consistent pattern to a flinch normal?

    Any thoughts greatly appreciated.

  2. #2
    Was this with or without a moderator??

  3. #3

  4. #4
    is the rifle bedded? what weight/profile barrel is it? any apparent pitting?

    off the shelf, I suspect it's nothing but a bit of heat-induced dispersion as the barrel flip under heat will offer an increasing POI, especially as after cooling, the next first 3 of the following group one-hole (ish) again...ie. after cooling.

    lateral dispersion on the other hand, is usually a sign of bedding pressure points in the receiver inlet on square sided actions.

  5. #5
    Quote Originally Posted by PKL View Post
    is the rifle bedded? what weight/profile barrel is it? any apparent pitting?
    Action is bedded. Sporter barrel (24 inch). No discernible pitting.

    The thing that is confusing me is that in the previous range session, this was not happening. Which leads me to suspect it is most likely operator error - but then I'm surprised at the consistency of this error!

  6. #6
    What difference is there in the way you use your bipod in the different situations. Because of the weight of abipod and the way it loads the stock it might be changing things.

    David.

  7. #7
    I did read a study on how people subconsciously tense up and start changing POI by holding the stock tighter and pulling the trigger a bit more after a few shots. So, whilst consistent, not unlikely to be operator error either. Could be interesting to take 3 shots, then let another person take the next 2 or three on the exact same target!


    Quote Originally Posted by Mungo View Post
    Action is bedded. Sporter barrel (24 inch). No discernible pitting.

    The thing that is confusing me is that in the previous range session, this was not happening. Which leads me to suspect it is most likely operator error - but then I'm surprised at the consistency of this error!

  8. #8
    If you are concerned about a flinch then try dry firing the rifle several times before shooting a group. Also try and get into your mind that the rifle will make the same noise, and recoil the same whether you flinch or not, the only thing is if you flinch it will have a negative affect on results.

  9. #9
    Might be a silly question but was it the same LOT of ammunition?
    I had the same problem with my Savage 308 and it was me. The first range session was fantastic! I screwed round after round into a ragged hole from a bipod -and I suck shooting from a bipod. The next session was about like the first. After that it went to hell for a bit because I was not concentrating on my technique as much. Had the "This is easy!" thing in my head which, of course, reared up and gave me a wet slap across the face, grouping wise. I knew the load was good so I just quit shooting groups. I would shoot at golf balls, or thumb tacks... anything but a group. It cured me. When I did get to a new load I was back to shooting as well as I ever do.~Muir

  10. #10
    Did the barrel get hot and did you let it cool down between groups?

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