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Is this normal?

Discussion in 'General Firearm Discussion' started by pirateer2007, Feb 9, 2010.

  1. pirateer2007

    pirateer2007 Spokane Wa Member

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    Both of these groups were shot at 100 yards with Federal Gold Medal Match ammo. The one in the center measured 1.75" and was shot with the 175gr GMM and the one in the top right measured .43" and was shot with the 168gr. Both were shot consecutively. The 1.75" group is a fair representation of all of my 3rd groups of this ammo which measured between 1.85-1.15. The average size of the 168gr was .55". All were measured center to center.

    My question is... Is that normal? I don't understand why 8gr of weight would make such a big difference. They were shot with a remington 700p using the standard 26" 1 in 12" twist barrel. The barrel was broken in properly.

    Any insight would be much appreciated!

    p.s. I also shot some 150gr Hornaday V-max and my average 3round groups with that measured .75"
     
  2. PhysicsGuy

    PhysicsGuy Corvallis, OR Resident Science Nut

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    Is the OAL the same on both rounds?
     
  3. pirateer2007

    pirateer2007 Spokane Wa Member

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    As far as I know, yes. Both were factory, bought on the dame day from the same shop. Standard .308Win.
     
  4. PhysicsGuy

    PhysicsGuy Corvallis, OR Resident Science Nut

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    Take a caliper to it, different bullet construction sometimes leads to leads with different OAL. Also there most likely is a difference somewhere else that you don't see. Are they both FMJ, or a small hollow point? (non expanding) Are they both boat tail? ect.
     
  5. pirateer2007

    pirateer2007 Spokane Wa Member

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    If I remember correctly, they were both BTHP Sierra Match King bullets. I will take a caliper to them as soon as I can find one to borrow :D But just setting both on the table, they look like they are the same exact length.
     
  6. DSbur

    DSbur Vancouver WA Member

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    OAL wouldn't have as much effect as the jump to the lands for where the ogive contacts them. Intuitively you would think that the less jump the better, but this shows the opposite. What I think is happening is the velocity/charge of the 168's is agreeing with the harmonics of your barrel better than the 175's.

    Federal Gold Medal Match bullets are Sierra MatchKings, they are a hollowpoint of sorts.

    175's may shoot just spiffy in your rifle, but just not at that charge/velocity.

    I'm currently doing 175SMK ladder testing on my .308 5R Remington 700. Charge weights from 42gr Varget to 44.4 gr in .2gr increments showed a definite progression of bullet placements vertically, but 42.9 showed a remarkable 'node' of accuracy with less than .75" vertical dispersion at 300yds.

    (The horizontal dispersion is from the nut behind the wheel...:eek:)

    The ogive of the 175SMK's is just a slight bit closer to the lands than the 168SMK, OAL's being the same FWIW.
     
  7. no time

    no time Roseburg area Active Member

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    Looks like you're all done buying 175 gr bullets....:)

    Sometimes rifles dont like certain bullets. i have a 270 that wont shoot boat tails, no matter how nice I talk to it...
     
  8. NoAim

    NoAim Hillsboro, OR Active Member

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    1/12" is a little slow of a twist for 175gr. It's probably not fully stabilized.

    As you mentioned, it should like between 147gr and 168gr.
     
  9. the4thshake

    the4thshake Portland Active Member

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    +1 on the twist not stabilizing the heavier bullets.
     
  10. BillM

    BillM Amity OR Bronze Supporter Bronze Supporter

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    This kind of ammo sensitivity is not at all uncommon. I've got a 30-06 that
    will shoot 165-168 ammo---ANY ammo--into 1.5" or less. Try to feed it
    150's and you are lucky if they all hit the paper.:)
     
  11. M.Link

    M.Link Guest

    From what I've been reading, the 175's thake longer to stabilize. At longer ranged the 175 "should" be as accurate, if not more. I have had my 700P do the same thing with my cousins hand loads to me, but at 200yds, the groups are very close, and out past that they are about identical. I have decided to stick to just 168s mainly, but I do have a box or two of 175s loaded up.