Bİg problem 7mm rem mag

Discussion in 'Long Range Hunting & Shooting' started by soundwaves, Jan 6, 2010.

  1. soundwaves

    soundwaves Well-Known Member

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    OK what the balistic programs say and some of you guys sugested was;
    a 7mm rem mag shooting a 175 grain PSP bullet at 2860 f/s it would hit 4 inch high at 100 yards and dead on at 300 yards. but went shooting today at an altitude at see level and it was 4 inch high at 100 yards and 4 inch low at 300 yards??????? going back to the 150 grain bullets from now on. can any one sugest me a good scope with balistic reticals that suits the 7 mm rem mag???? thanks guys
     
  2. jeffro

    jeffro Well-Known Member

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    Is the 2860fps off the ammo box, or did you chony it for the speed.
     

  3. soundwaves

    soundwaves Well-Known Member

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    no a balistic program gave me that speed. the load is PMC 7mm Rem Mag 175 grain PSP. maybe thats not the speed. any ideas for a scope whith balistic reticals that suit 150 grain 7MM REM MAG? (not to expencive but good scope for long range)
     
  4. RBetts

    RBetts Well-Known Member

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    check your scope height and measure your velocity don't guesstimate
     
  5. MudRunner2005

    MudRunner2005 Well-Known Member

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    I prefer the 160 grian Barnes Triple-Shock bullets out of my 7mm Rem Mag. They fly the best out of all the 7 Mags I've had. They don't make the exact ones I shoot anymore. Federal used to mass produce them, and they're part number is P7RK. You oughta check them out.
     
  6. MontanaRifleman

    MontanaRifleman Well-Known Member

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    Something is not right here. No way should your bullet should be hitting low @ 300 yds if you are 4" high @ 100 yds.

    A 175 psp should have a BC of at least .5 and using that and 2860 fps (which is a very reasonable guess of actual velocity) I am getting a 310 yd zero with bullets 4" high @ 100 yds @ 5000" elevation. I'm alos using 1.8" sight height.

    The 150's will shoot flatter.

    I think most BDC reticles are calibrated for about 3000 fps which should be close to factroy 150's.
     
  7. angus-5024

    angus-5024 Well-Known Member

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    What's the best way to accurately measure scope height?
     
  8. azsugarbear

    azsugarbear Well-Known Member

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    Leupold and Swarovsky are two scopes with good quality that offer ballistic reticles. Some slightly less expensive scopes with ballistic reticles are Weaver and Nikon. The Nikon is different in that it uses circles for drop compensation on the vertical crosshair. These types of reticles are designed as a "one size fits all", which is usually OK out to 400 - 500 yds. Beyond that, there are just too many variables that can effect accuracy - so that it usually all the further the gradations will take you.

    Scopes with MOA or mildot gradations can be much more accurate and will take you out a lot further. I am not aware of all the scopes that offer such a reticle, but Nightforce ($$$$) is one.

    Perhaps the best route would be a used Leupold VX-III with a target turret installed and an elevation dial from Leupold Custom shop or Kenton Industries. With an accurate drop table, it can take you out well beyond 100 yds. Good luck.
     
  9. MontanaRifleman

    MontanaRifleman Well-Known Member

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    I measure the outside diameter of the objective bell, then measure the OD of the barrel just below were I measured the bell, divide those measurements and add them to the distance between the bell and barrel.
     
  10. angus-5024

    angus-5024 Well-Known Member

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    Montana Rifleman,
    Thanks. I always wondered the right way to do it. So I am assuming that you do this with the stock removed?
     
  11. MontanaRifleman

    MontanaRifleman Well-Known Member

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    You could remove the stock, but I can get an OD on the barrel with stock on.
     
  12. RBetts

    RBetts Well-Known Member

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    With the rifle out of the stock
    Measure objective bell divide in half
    Measure the barrel dia at the same place you measured the Objective bell and again divide in half
    Measure the distance from the top of the barrel to the bottom of the Obj. bell
    add the 3 numbers and that is your distance
    With the rifle in the stock remove the bolt half way measure from the top of the bolt to the bottom of the scope.
    Now just measure the diameters of both the bolt and scope at that point and divide by 2 add all three #'s and you have the same dimension.
     
  13. fmajor

    fmajor Well-Known Member

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    Hey soundwaves -

    Back to your *initial* problem..... If a ballistics program calcs your bullet drop, given all the information, and your actual performance is different, something obviously isn't right - distance(s) to the targets for drop measurement, *actual* muzzle velocity, temperature, load data, etc.

    Do you personally know for sure the velocity of your round (as asked earlier?) via chronograph? The stated velocities on ammo boxes are acheived by specific test barrels in specific conditions. Mostly they are exaggerated from *actual* 'production' firearms. This would explain why your round is soooo low compared to what it *should* be.

    Otherwise and in general, i'd not be too reliant on a BDC scope unless you can adjust that compensator for each round/lot of ammo you shoot (again lotsa variables). Hard data for each lot of ammo you shoot is as simple as recording the actual results you personally get and forget what the round is *supposed* to do - know your ranges/drops via personal observation.

    frank
     
  14. liltank

    liltank Well-Known Member

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    Hey MR,

    If you reread his post, he stated he sighted in at sea level. Your drops are probably right for 5000'. He stated originally that he was going to be hunting at that altitude, but not sighting in at sea level. That is 5000' of elevation variance. Just a thought. I have been following this and everything that I know of is correct. There was something we were missing and I believe that to be the problem.

    Tank
     
    Last edited: Jan 7, 2010