Got a real brain buster

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Tikkamike, Nov 10, 2011.

  1. Tikkamike

    Tikkamike Well-Known Member

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    I have a buddies Sako 75 in 7STW the rifle has been taken great care of as far as cleaning and such. I worked up a load for him with 168 bergers and it didnt shoot great but it would hold a 1" group easily. but he said it was good enough so I let it be. Few months later after shooting it a few times he calls and says it is shooting 8 " groups. So i went and got it and checked the obvious things, action screws, scope mounts to gun and scope. went and shot it and got about 3" so I tried a new set of sako optilocks and 3" groups, so I changed scopes to a scope i know is good and still 3" groups. so I loaded up bergers close to the lands thinking maybe they were too far away being loaded to fit the sako magazine... still 3" groups. so I tried partitions and 3" groups again. so I took it to the gunsmith and had it bedded went and shot it and yet again 3" groups.. the rifle has less than 100 shots through it. so I checked the crown its good, bolt lug recesses are good and clean and lugs have good even contact. stock does not appear to be cracked and everything appears to be fine. what do I check next? the rifle used to shoot why will it not now? maybe he shot it with debris in the barrel and now there is a slight bulge? I have run tight patches down it and it feels fine.. no loose spots. Someone help me out give me some ideas. I am tempted to send it to hill country in texas or just tell him to have the thing rebarrelled and gone over while its in pieces.
     
  2. MTBULLET

    MTBULLET Well-Known Member

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    it's been my experience that bergers tend to "copper foul" faster than other brands. i still use 'em in rifles that like 'em, but use "wipe out" frequently.
     

  3. Tikkamike

    Tikkamike Well-Known Member

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    i use wipe out and boretech eliminator and bore scope the bore and its CLEAN still shoots like poo
     
  4. Boss Hoss

    Boss Hoss Well-Known Member

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    Check PM
     
  5. Mikecr

    Mikecr Well-Known Member

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    Did you work up a load with new brass?
     
  6. Tikkamike

    Tikkamike Well-Known Member

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    It was new when I started
     
  7. theflyonthewall

    theflyonthewall Well-Known Member

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    Have either of you ran any different bullets through it other than THAT particular lot of Bergers? I know it's rare for good companies to have a bad run of bullets and let them get all the way to retail, but you've already covered most of the obvious issues.

    So what's left....hmmm?

    1. Rifle wants a different bullet.

    2. As the barrel heats, could it be contacting the stock---even though it may not do so when cold?

    3. Has headspace been verified?

    4. What's the twist rate of the barrel? Surely it's fast enough to stabilize the 168's, but is there a tiny chance that it's been rebarreled at some point?

    5. Other than that, I'd have to say to slug the barrel and mic the slug to make sure that the tolerances inside the barrel are up to spec.
     
  8. prariehunter

    prariehunter Member

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    Well Mike I believe your story because the exact same thing happened to my buddy last year in Alberta. Exact same sako 75 7mmstw that used to shoot 160gr barnes tripple shocks into 1/2 inch. But when the big berger bullet craze came up here we had to shoot them. So we tried a pile of different powder charges and seating depths and nothing shot at all they were horrible, but when he went to switch back to barnes bullets they then shot the same 3 inch groups. We cleaned it and tried a differnt scope as well nothing worked so he sold it. For your buddy I will bet that nothing short of a rebarell will help.
     
  9. Loner

    Loner Well-Known Member

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    Check the end of the bore with a ball gauge and mic it. And just out of curiousity, did
    you work up a new load for the once fired brass? The original 7stw brass was 8mm brass.
    It specs slightly larger in front of the belt. The whole industry went with 300 mag spec
    brass in that dimension and the cases really expand a lot on that first firing. Guys routinely used to chamber 7mm to stw and they would always clean up. I have some of
    the old brass unfired and you couldn't chamber it in a newer tight chamber. I would
    guess that Sako is true to the original specs.
    You will find the specs to be .513 for the stw and .511 for the
    H&H 300. That extra .002 of expansion may be enough to really drop your speeds.
     
    Last edited: Nov 11, 2011
  10. Trickymissfit

    Trickymissfit Well-Known Member

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    I was thinking the same thoughts. I'd slug the barrel, and gently push the slug thru the barrel looking for tight spots and loose spots. I'd like to think the last two or three inches of the barrel has opened up about a half thousandth of an inch. If the barrel is slightly in the tight side and then gets slightly looser at the muzzel end it will never group well.

    A few years back a buddy of mine ran a 7STW reamer thru a factory Remington 7mm mag. The rifle shot very well, and was capable of 750 yards kills. He liked it so well that he had Ron Pence do another Remington barrel for a Sendro, and it probably had another hundred yards on the factory barrel. About the time he got the Sendro going well the other started to go south. It was the muzzel! How well the Pence barrel lasted I don't know as I have not spoken with Tony for awhile.
    gary
     
  11. trebark

    trebark Well-Known Member

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    Mike, I had a factory Rem700 Mountain Rifle in 280 that showed similar behavior as your 7stw. It would shoot 1moa at times but more often than not, it shot 3 or 4" at 100. I tried everything, trigger job, bedding, pillars, different bullets, different powders, different primers, new HS Precision stock (bedded)...everything. No matter what I did, I could not get the gun to shoot. Finally, sent it off to Hart Rifle Barrels and had it rebarreled which included truing the action and new bedding. Now the rifle will shoot.

    http://www.longrangehunting.com/forums/f53/my-280-updated-32771/

    I hope it doesn't come down to this for you, but it sure sounds like it.
     
  12. screech

    screech Well-Known Member

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    Had a 243 in a winchester coyote. Would shoot all right then crap. After I rebuilt it into a 264 asassin it shoots great. Id guess a new barrel, blueprint and a bedding job is in order my friend
     
  13. Trickymissfit

    Trickymissfit Well-Known Member

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    you don't always need a new barrel. If you have a 26" barrel in the .243, you could have cut a new chamber and maybe wacked an inch and a half off the muzzle. 243's are well known to be hard on throats, so you could just take about an inch off the big end, and rechamber it. A 243 would see much difference with a 24" barrel verses a 26" barrel, and probably would group more consistent. In your case it would have been interesting to see what you did actually cured the first problem.
    gary