What Variable to change Wen truing my Weapon at Extended Ranges

Discussion in 'Extreme Long Range Hunting & Shooting (ELR)' started by seidersjoden, Dec 23, 2013.

  1. seidersjoden

    seidersjoden Well-Known Member

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    When doing the truing process I have heard different opinions. Some say after sighting the gun in at 100y then shooting out at 900-1300y or whatever range you can consistently hit targets at, if the group is high or low to adjust the MV. Some say if I have Chronograph the gun and feel confident in the MV that I should change the BC. By the way I’m shooting the 230 Target Hybrids. Some people lean toward changing the MV over the BC when truing a weapon or vice versa. So my question is, if I do a good chrono of a weapon and take as many variables as I can out of the inputs I put into my Kestrel Atrag, which one should I change when truing the weapon to match the scope value?

    Thanks,
    Joden
     
  2. royinidaho

    royinidaho Writers Guild

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    It may well take a little of both.

    If you are fine tuning, which is clay birds to beyond 1K, you'll find your muzzle velocity will not be what your chony says it is and your bc will not be what is published.

    Different barrels have slightly different bc values so if you and your buddy are shooting the same bullet in the same cartridge using the same bc will get you close but is that close enough?

    Another input to be concerned with is the difference between line of bore and line of sight that is, sight height. If your scope base isn't canted this can be measured. If canted, measure then calculate the fudge factor.

    Bringing at least these things into alignment will get you where you want to be.
     

  3. seidersjoden

    seidersjoden Well-Known Member

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    Great, thanks for the clarity Roy. I mess around with both.
    Joden
     
  4. osoh

    osoh Well-Known Member

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    I have seen folks tweak their systems trying to make sense of the trajectory and their programing so that the adjustments and point of impacts actually work. But they either end up with a velocity that is not true or they think the BC is better than what it’s rated at.

    Just something I check on any new scope, doesn’t matter what mfg. before or while mounted on the rifle.

    I have an area that has been marked with a true measured 100 yards, using a 100’ tape not a laser. Then I hang a 72” carpenter’s rule that has been checked with a caliper for true readings. Sounds dumb but you would be surprised how some rules of this type are off a bunch by the time you get to 72” kinda like some scope travels as fallows.

    Make sure the rule is hung or mounted true vertical with a level.
    You can also take a fine point Sharpie and mark all the mil settings using your caliper, so you’re ready for moa or mil reticles for testing.
    The most time consuming part is setting up the first time.

    Now that you have the range measured and the carpenters rule checked, marked and hung true vertical, you can either take a piece of steel square stock equipped with a picatinny rail held in a vise solid ready to mount the rings and scope on or a solid gun vise of some sort for securing the complete rifle. I like the solid piece of steel stock for clamping down tight in the vise to eliminate any chance of movement with the scope.

    Whatever method used, secure the scope or rifle equipped with the scope while having the scope reticle aiming at the top edge of the rule while set at zero.

    Now turn your elevation turret and make notes as to how much every click of the turret moves on the rule. (In some cases another person with a pointer down by the rule and using radios will be helpful)l. As you adjust your scope’s elevation turret pay attention to the error. Try this a few times to make sure your still at zero when dialing back up to the top of the rule in case your scope or gun may have moved while testing – it’s all about good info

    You will see any amount of error really start to add up as you get to your max travel or 72” on the rule. Take the info you have and check with your ballistics program to change the value of your clicks in your scope info you entered into the program,

    Cause for all this is the tolerances in the machining of the threads and or wear in the turret travel.
    I have seen some dumbfounded looks while doing this quick exercise, it’s nice to know that when you dial in 10 or 25 mils that you really do have 10 or 25 mils not 11.5 or 28. Same goes for folks with moa adjustments a 1/4 moa is a true 1/4 moa or 10 moa's when dialed.

    This simple test cleans up questionable speeds and BCs and helps with making drop charts that are true as far as corrections needed.

    Another thing as long as the level bubble on the scope or rifle is true, you should be able to dial the full vertical travel adjustment and travel down the rule without veering off course some, if it does move your turret/scope reticle is not plumb with gravity.

    It’s all the little things that add up and make a big difference in time.

    I do get a little long winded at times

    Cheers
    oneshot.onehit
     
  5. seidersjoden

    seidersjoden Well-Known Member

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    All great info, thanks for the tips
     
  6. redneckclimbing

    redneckclimbing Well-Known Member

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    Roy-

    I know that this is an old post, but I hope you could still answer a question. If the scope base is canted, which part do you measure to, and what is the fudge factor you refer to?
     
  7. seidersjoden

    seidersjoden Well-Known Member

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    Another input to be concerned with is the difference between line of bore and line of sight that is, sight height. If your scope base isn't canted this can be measured. If canted, measure then calculate the fudge factor.

    Bringing at least these things into alignment will get you where you want to be.[/QUOTE]



    Im curious about this too. For example, I have a 20MOA base, are you saying that I need to measure from the front of the scope for proper scope height or from the middle of the scope. I would think the front but could be wrong.

    Joden
     
  8. Tumbleweed

    Tumbleweed Well-Known Member

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    Im curious about this too. For example, I have a 20MOA base, are you saying that I need to measure from the front of the scope for proper scope height or from the middle of the scope. I would think the front but could be wrong.

    Joden[/QUOTE]

    I measure at the middle of the scope tube as I also have a 20MOA base. Measure the gap between the bolt and bottom of the scope tube. Add this measurement to half the bolt diameter and half of the scope tube diameter and you'll have your sight height.
     
  9. idaho elk hunter

    idaho elk hunter Well-Known Member

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    I have done this in every way possible since my first "precision" rifle that I owned 58 yrs ago. I can tell you if you want to simplify the learning curve and save some headache of tuning then the Burris Eliminator is second to none.
     
  10. seidersjoden

    seidersjoden Well-Known Member

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    I measure at the middle of the scope tube as I also have a 20MOA base. Measure the gap between the bolt and bottom of the scope tube. Add this measurement to half the bolt diameter and half of the scope tube diameter and you'll have your sight height.[/QUOTE]

    I have to ask, what made you think of doing this, were corrections on a ballistic calculator not correct and you assumed it was an incorrect input of sight height?

    Thanks,
    Joden
     
  11. seidersjoden

    seidersjoden Well-Known Member

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    Using the burris doesn't solve the sight height problem, plus try shooting the burrris out past 1000y with only a 12 power objective lens. Just my thoughts

    Joden
     
  12. 4xforfun

    4xforfun Well-Known Member

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    First off...don't get all hung up on scope height. Assuming a 300 yard zero. If I am off by 1/2 inch...say 2.0 instead of 2.5 inche scope height.....a HUGE error, my impact only changes 1.2 inches at 1000 yards.... 1/10 moa!!

    So don't sweat the small stuff.

    Now, that being said..I STILL like to know.:D


    So....1/2 diameter of action. That is easy......Take remington 700's and 40XB's...1.35 inch. Divide by 2 = .68. Just measure your action or look it up and divide by two.


    PLUS


    1/2 scope TUBE diameter say a 30mm tube... 1.18 devided by 2 = .59 inches.


    PLUS

    Measure the distance from the bottom of the scope base (where the base contacts the top of the action) to the bottom of the scope ring where the bottom of the scope rests in the ring..... lets say for this case is 1 inch.

    So.... .68 + .59 + 1.0 = 2.27 inches.

    If you have a 20 , 30, or whatever MOA base, and you are truly, truly ANAL......measure BOTH the front and back ring/base height and divide by two and use that number. But really.......come on!!

    Simple math. :D
     
  13. seidersjoden

    seidersjoden Well-Known Member

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    All great info thanks 4xforfun
     
  14. seidersjoden

    seidersjoden Well-Known Member

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    Simple math. :D[/QUOTE]

    So 2.27 inches should apply to me because I have a rem 700 action and 30mm tube right?