Need some ballistics help - Weirdness

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by bhtkevin, Aug 14, 2012.

  1. bhtkevin

    bhtkevin Active Member

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    Mar 28, 2012
    OK so my buddy has a custom MG Arms 300 Win Mag and we are practicing for an upcoming Ibex hunt but his rifle is doing something weird.

    100 yards: +1.5 inches... 3 shot sub-1" group

    No adjustment to the scope, move to 200 yards...

    200 yards: +2.0 inches... 3 shot sub-1" group

    Huh? According to every ballistics table it should be +1.5" at 100 yards and around zero at 200 yards. Any ideas what could cause this? I am going to shoot the gun next time and see if I have the same results and we are also going to back up to 300-400 yds.

    Side note... We are shooting off of a lead sled in the prone position for now until we are comfortable everything is sighted in and working as expected.

    Thanks much,
    Kevin
     
  2. rscott5028

    rscott5028 Well-Known Member

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    You said "no adjustment to the scope."
    Is the scope adjustable for paralax?
    Did you adjust it?

    Did the shooter move to a new position?
    Or, did you shoot at a new target another 100 yds out from essentially the same position?

    Was the sun rising and heating rapidly and/or ammo sitting in the sun between shooting the 2 groups?

    -- richard
     

  3. bhtkevin

    bhtkevin Active Member

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    Good ideas...

    I dont think the scope has a parallax adjustment but that is a good thing for us to keep in mind. He moved back to 200 yards (target stayed) and I dont know if he was in the exact same position both time. I will find out. I know that the mirage effect is pretty extreme right now from the last time we shot.

    We are going back out Saturday so we will watch these things more carefully the next go around.
     
  4. Lefty7mmstw

    Lefty7mmstw Well-Known Member

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    Sounds like your input for the scope to bore center is off. It only takes a couple tenths on an inch to make a rifle seem a lot flatter shooting than it is. At least it isn't the other way for you. Greater distance between the scope and bore than estimated will make it look flatter shooting. Lesser distance will make it look as though it's arking more.
     
  5. bhtkevin

    bhtkevin Active Member

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    Went and shot this weekend and was dead on back to 400 yards. I think it was eitheR parallax or shooter error. Seems to be on now. Both of us were sub moa at 400 yards shooting in an awkward position. I'll be happy once I can get to 500 and put it in a paper plate with wind. Its going to take more practice to read the wind properly.