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Thread: One For Our Engineers

  1. #1

    One For Our Engineers

    I have a Sako 75 in .243, which is eight years old and owned from new. It fires 100 to 150 rounds per year so has fired no more than 1,500 absolute max. It shoots very well with home loaded ammunition, loaded to sensible limits. It has never fired hot loads. It is cleaned properly etc.

    When I bought the rifle, I measured the overall length to the origin of the rifling, using a RCBS precision micrometre. The reading was +135 so after the usual working up and trying different settings, I settled on +125 bullet depth seating, thus giving ten thousands of an inch clearance.

    Yesterday, for some unknown reason, I decided to measure the rifle again. I found that the measurement to the origin of the rifling is now +140, so 5 thou' longer than when new.

    QIs this normal wear and tear ?

    Q As there is no deterioration in accuracy, would you leave the bullet depth setting as it is or try setting it out another 5 thou' ?

    As its not broken, I am tempted to leave well alone. What do you think ?

  2. #2
    Have you used the same micrometer in exactly the same way?

    If not the same mic, is whatever you used "in calibration"?

    If you are not used to precision measuring tools, it may be a technique issue.

    On the other hand, you may have "run in" your rifle.
    "Nonsense! They couldn't hit an elephant at this dista.....................".

  3. #3
    Quote Originally Posted by charadam View Post
    Have you used the same micrometer in exactly the same way?

    If not the same mic, is whatever you used "in calibration"?

    If you are not used to precision measuring tools, it may be a technique issue.

    On the other hand, you may have "run in" your rifle.
    Yes it is the same tool, which is pretty basic.
    As far as technique is concerned, I think I am being consistent. However as a person who got thrown out of the woodworking class at school for 'lack or aptitude', anything is possible .

  4. #4
    i used to worry myself about things like this. Now i just log any change and carry on as normal you know the score "if it aint broke" your rifle will let you know if theres somthing wrong.

  5. #5
    "As its not broken, I am tempted to leave well alone. What do you think ?"

    Do you really need to ask Norm? You've answered your own question, it's not broken.
    It's the calibre of the shooter that counts not the calibre of the rifle.

  6. #6
    Leave it be.
    Quit needless measuring of things.
    Sleep better.~Muir

  7. #7
    After 1500 rounds the barrel will definitely have worn a bit from the corrosive gases if nothing else. Presuming you've used a OAL gauge with the same bullet then its probably a real result but nothing to worry about. Given you've not noticed a reduction in accuracy then I'd probably leave it alone but there'd be no harm in trying a few rounds at varying depths. If you didn't use the SAME bullet each time it could easily be a difference in the bullet tolerance - I've had batches of Sierra MatchKing Palma's that vary but significantly more than 5 thou! Oh and the SAAMI spec for 243 has a min to max COAL tolerance of 4.3mm!!!

    I tend to check the OAL of my (and the wife's) rifle every year and then adjust my homeloads to maintain a 15thou jump but then again we're shooting 1500 rounds + a year and you tend to notice a drop off in accuracy at 1000 yrds +!

  8. #8
    Reminds me of a witicism from an American roughly stating "many a good rifle was ruined with a chronograph".

    I don't even have a method of measuring OAL or throat depth.
    Brian.

    Just because you are paranoid, doesn't mean they aren't out to get you......

  9. #9
    Quote Originally Posted by Claret_Dabbler View Post
    Reminds me of a witicism from an American roughly stating "many a good rifle was ruined with a chronograph".

    I don't even have a method of measuring OAL or throat depth.
    True that. I have one for cast bullets but never use it for jacketed.~Muir

  10. #10
    Uncle Norm
    There is nothing wrong with measuring the rifle - you have the tool & have clearly used it well - you now know that the rifle is wearing - at a typical rate for the usage. The bullets clouting the end of the rifling and the hot gasses ripping past is bound to erode it thus. - Your rifle ain't bust - just run in. It is exhibiting normal wear & tear.

    The rifle shoots well now so don't f*k about worrying if the sanctified (& bunkum IMHO) 10 thou jump has now gone to 15 - just enjoy shooting it!
    What has not changed is the volume inside your cases which is set by your seating depth & this is probably why it still shoots like it used to.


    Ian

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