Figuring Drop based on "Come Ups"?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Misfire, Nov 17, 2008.

  1. Misfire

    Misfire Well-Known Member

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    How do I convert my "come ups" to inches of drop at a given range?

    I've been doing this the "Redneck" way by going out to the range and shooting for zero at each distance. I have not progressed to software yet and at the distances I typically hunt (to 500 yards) this methods works.

    So if I have a 100 yard POA/POI zero and have to dial 3 inches (12ea 1/4" clicks) to zero my rifle at 300 yards, how to I convert that to inches of drop at that distance? Is it as simple as 3" of drop or is the drop a different variable than the come up?

    I know this is a total noob question so thanks for any input.

    Thanks,

    Chad
     
  2. WildcatB

    WildcatB Well-Known Member

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    If your scope is 1/4" per click at 100. It will be 1/2" per click at 200, 1" per click at 400 and 1.25" per click at 500.

    To work out intermediate distances, multiply the distance you're shooting by .0025. Then multiply that answer by the number of clicks you have worked out for that distance.

    For example 350 yards would be 350 x .0025 which is .875 inches. Each click comes up .875 inches. Now say you had 12 clicks at that distance, your come up in inches would be 12 x .875 = 10.5 inches

    Hope this helps.
     

  3. WildcatB

    WildcatB Well-Known Member

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    oops didn't answer the 300 yard question.

    At 300 a click is 300 x .0025 which is .75"

    Multiply that by 12. Which is 9, or 9 inches up.
     
  4. Longshot38

    Longshot38 Well-Known Member

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    The easiest way to do what you are talking about is to stop thinking in terms of inches and start thinking in terms of MOA. MOA or Minute-of-Angle is a unit of measure that is relative to distance. In other words 1 MOA is equal to 1.047 inches (just round to 1 inch) at 100 yards. Thus if your scopes turrets are set at 1/4 inch click then it will move you POI 1/4 inch at 100 yards (or 1/4 MOA)

    Now that you get the concept of MOA we go back the idea of MOA being relative to distance. In other words @ 100 yards a MOA is equal to 1 inch, @ 200 yards it is equal to 2 inches , @ 300 it is equal to 3 inches, etc...... An you also know that you scope moves your POI 1/4 moa per click. With these values it becomes easy to figure out how far you are moving you POI for a given range. You just multiply the number of MOA you move you POA by your MOA value for your given range. So if you have to move you POI 16 clicks (4 moa right) for 300 yards then you would have changed your POI 12 inches (4 moa times 3 inches). See that easy.
     
  5. Misfire

    Misfire Well-Known Member

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    Thanks guys!

    Good info!

    .
     
  6. devildoc

    devildoc Well-Known Member

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    Well good information has been given so far; but in my opinion, not complete information.

    It depends on how your scope is calibrated: many scopes are calibrated so that one click equals 1/4" at 100 yards, many others are calibrated so that one click equals 1/4 MOA at 100 yards. To complicate matters, some scopes are 1/8th or 1/10th inch/MOA at 100 or 1cm/click at 100. And in truth; especially with low to mid grade scopes, what they are supposed to be calibrated to and what they are actually calibrated to can vary quite a bit.

    So,.......Shoot a group or ten at 100yds, adjust your scope 4 clicks up and repeat. Then, if you're a really anal type move to 200yds and repeat. Do the math and figure out what one click on your scope is equal to.
     
  7. Misfire

    Misfire Well-Known Member

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    The two primary scopes I'm concentrating on are both Leupold Mark 4s.

    The first is a Mark 4 PR (1" tube) with 1/4" clicks for both elevation and windage. This scope is mounted on my AR and is mostly a varmint/plinking gun. I have "dopes" out to 300 yards and the rifle shoots like a dream out to that distance. While I don't plan on doing any serious hunting much past that distance I still want info to accurately shoot it as far as possible.

    The other is a Mark 4 LRT (30mm) tube with M3 knobs 1" click elevation and 1/2" click windage. This scope is mounted on my more serious big game rifle. The rifle is a Sendero in 7mm Mag. It has proven to be quite accurate out to 500 yards. With the click variables that have been mentioned here I'm worried that the 1" elevation may be too much for accurate shooting past 500 yards. The only way I can be sure is more range time and shooting at those longer distances to see exactly how far off the 1" clicks will be from POA and if they are too rough to really get out to say 700 -1000 yards.

    .
     
  8. Longshot38

    Longshot38 Well-Known Member

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    Both scopes being MK4's they should track well and as precribed. Leupolds are known for shooting the box well.

    As for the adjustments. The PR being 1/4" @ 100 will be roughly 1/4 moa adjustment and should work just fine. Your LRT should be fine also. Remember that the vitals are a 12-18" target on most game. And with your M3 turrets you are moving 1 moa per click. Even at 1000 yards it is only 10 inchesThus you should be fine. However I think I would eventally change them out for some M1 turrets.
     
  9. jwp475

    jwp475 Well-Known Member

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    One needs to know wheter or not his scope adjust in Inches Per Hundred Yards (IPHY) or Minutes Of Angle MOA. Thier is a significant difference between the 2 at 1K
     
  10. lever-hed

    lever-hed Well-Known Member

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    misfire,
    all the info is good. You should zero your rifle for 100 yds at that particular ammo, load, bullet, etc. Then, once your satisfied with that zero, practice shooting at 50 yd increments all the way out to what ever distance your shooting at.. this will giv you ACTUAL drop for each distance (and record it)and your dope chart will be all the more accurate. You could run the numbers thru a ballistics calculator but actual shooting will be reality and what you want.. further, your zero could be 3 or 4" high/center at 100 yds if you tend to shoot at very long ranges 400 yds or so. bottom line, dope it to what yardage you typically take shots at.. have a good day.
     
  11. lever-hed

    lever-hed Well-Known Member

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    ..in all honesty, "dialing in" wa snever my forte, In the heat of the moment I point and pull the trigger, too much calculation at the point of attack is not meant to be. I fyou know your rifles zero and POI at various yardags that's all I use to hold over/and windage, is all I'm saying.
     
  12. WildcatB

    WildcatB Well-Known Member

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    This works as long as you don't significantly change elevations. I sight in at 5000 ft but often hunt above 8000 ft. That 3000 ft elevation change gives a 14" difference in bullet drop at 1000 yards. You have to put some trust in your calculator and barometer. However, it is still important to practice at different distances and elevations to confirm that your ballistics calculator is accurate.
     
  13. WildcatB

    WildcatB Well-Known Member

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    How far do you shoot this way? My 1000 yrd drop at 5000 ft elevation is 255 inches. How do you hold 255 inches high? That's 21.25 ft. Of course you could use mil dots but my scope only has 4 dots below my zero. I HAVE to dial to shoot anything beyond 700 - that's where my 4th dot is. When shooting at animals, I'd rather hold right on with no guessing, so I usually dial everything beyond 250 yards. I normally have plenty of time because at longer distances the animal is often undisturbed. That's one of the major benefits of long range hunting.
     
    Last edited: Nov 19, 2008
  14. jwp475

    jwp475 Well-Known Member

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    Turrets man, turrets. I dial in my needed corection for the distance being shot and aim dead on.

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