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Old December 16, 2017, 06:18 PM   #1
DMiller23
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200 ZERO

Got a few questions after shooting today that I can't figure out why.

First off I'm shooting a Howa 1500 barreled action in 7mm R.E.M. Mag. Shooting 150grn. Winchester power points. (Was just shooting this factory ammo up fire forming brass) I put a new leupold VX 3 2.5-10x50 on it today.

I bore sighted the gun at 40 yards then backed up to 100 and sighted it in for an inch and a half high. (Zero 200) backed up to 200, shot a 5 shot group of roughly 2 inches. Center of the grouping being 8 inches high. Went back to 100 and zeroed at that yardage. Back to 200 and now I'm still 6-7 inches high. No to very little wind, shooting downhill about 6-8'.

I'm at a loss why it's doing this. In years past with other rifles (and hand loads) I own when shot at 100 yards an inch and a half high it's zeroed at 200. At 300 it's about 3.5 low. Is it the elevation change causing me to shoot higher. To me it seems it breaking the laws of gravity.

Also had a buddy shooting his 30-06 and he had the same exact results that I did. Does shooting down or up hill that little make that big of a difference?
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Old December 16, 2017, 11:48 PM   #2
HiBC
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What I do: I'll use a short range "so much high" preliminary zero to get me on paper at the longer range,but if I want a 200 yd zero,I actually zero at 200 yds.

I'm guessing what you may be running into is another variable caused by sight height.General rules of thumb are an OK guideline.

There are ballistic calculators where you can enter specific parameters and get results that will probably be quite close. And,you can actually enter the up/down slope of your shot. FWIW, the slope is not your problem.
The short explanation,the slope is part of a right triangle. While your perceived range is the hypotenuse of the triangle,what gravity has to work with is the long leg of the triangle. That's a little shorter than the hypotenuse,and that difference in "range" is what has an effect on elevation.
If you had 10 feet of elevation change over 200 yds,the effect on target would be negligible.You can figure it more than one way,but A squared +B squared =C squared works . Hypotenuse=600 feet squares to 360000. Slope,10 feet,squares to 100. Subtract the 100 from the 360000 So the range gravity is working on your bullet is the square root of 359900...which is 599.917 feet.I doubt you measure the range that close.

Come up with your bullet "Ballistic Coefficient",velocity,and how high your crosshairs are above the center of the bore,then go here for a free calculator you can use,compliments of Hornady

https://www.hornady.com/team-hornady...alculators/#!/

There is a selection for basic or advanced..or something like that,you can enter slope,wind,etc in advanced. Play!! Change things and see the results.
You might want to look at a 300 yd zero.. Fun tool you can learn a lot from.

It will even offer you a small "cheat sheet" range card you can print off.

Last edited by HiBC; December 17, 2017 at 12:17 AM.
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Old December 17, 2017, 05:25 PM   #3
JohnKSa
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Quote:
Is it the elevation change causing me to shoot higher. To me it seems it breaking the laws of gravity.
Significant elevation difference between the shooting position and the target WILL make the bullet hit high.

But 8 feet of elevation difference over 200 yards isn't significant. I agree with HiBC, it is negligible. The correction factor applied to the range would be a tiny fraction of an inch.
Quote:
I'm guessing what you may be running into is another variable caused by sight height.
That's a good place to start. How high is the center of your scope objective lens above the center of the bore?
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Old December 17, 2017, 10:08 PM   #4
DMiller23
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Sightline to bore is 1.875. I shot again today with a couple different hand loads that I'm getting dialed in for this particular rifle. Today I shot at my range where there is no to very little elevation change. I did not adjust the scope from yesterday and had the same results today. After fine tunning my load I went back out and shot a few more times at 100. 1.5 inches high. Back up to 200 and again I'm 6 inches high
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Old December 17, 2017, 10:10 PM   #5
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For some reason all of my reply didn't post. Anyways I got it tuned in and figured out now. Thanks for the help and the ballistics calculator link!
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Old December 17, 2017, 11:44 PM   #6
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Dmiller it would seem that if you follow the ballistics charts the trajectory of the bullet would be about 2" high at 100 yards for a two hundred yard zero. The problem here is now your line of sight at 200 yards will be the same as at one hundred but for one significant difference. You are aiming higher at one hundred so trajectory changes as the barrel is aiming higher. Based on the type of mounts and the height of the cross hairs this two will affect you point of impact. It is easier to adjust you scope elevation to zero at 200 yards knowing that at 100 yards the impact will be 1/5 to 2 inches higher but not the other way around. HIBC has given you a lot of great information.
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Old December 18, 2017, 10:24 AM   #7
Jim Watson
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Be nice to know what "tuned in and figured out" amounted to.

I figure that a 200 yard zero should be determined by shooting at 200 yards and adjusting sights to suit. Short range zeros to get on paper are not otherwise reliable.
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Old December 18, 2017, 12:18 PM   #8
T. O'Heir
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"...shooting downhill..." That'd the issue. Up or down hill changes the POI.
"...At 300 it's about 3.5 low..." Winchester Factory 150's, when sighted in 1.4" high at 100, should be 6.6" low at 300. According to them.
"...= C squared works..." For a right angled triangle only. The "Ballistic Coefficient" has nothing to do with it.
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Old December 18, 2017, 01:37 PM   #9
HiBC
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Mr O,once AGAIN,you are just plain wrong. Snicker.(Mr O's signature snide comment. I figure he'd appreciate being on the receiving end of it)

The Pythagorean Theorum applies because the horizontal distance,the vertical distance,and the bullet path make a right triangle.

And I provided the math to demonstrate that 10 feet elevation over 200 yds is insignificant.

I'd appreciate it if you can show me the math that backs up your claim. Snicker.

I provided the OP with a link to Hornady's ballistic software resource. With it he can model his trajectory by entering key parameters.By varying those parameters and re-running the model,he can learn a great deal about ballistics. The ballistic co-efficient is one of the key parameters.The OP expressed appreciation for the new tool.

Your post indicates you lack understanding of ballistic software and how Ballistic Coefficient,velocity,and sight height are basic inputs.

But if you ask me nice ,I'll walk you through it. Snicker.

Mr OP,something you might clarify. There is a 7mm Rem Magnum,and a 7mm R.U.M (Remington Ultra Mag) Which are you using?

Last edited by HiBC; December 18, 2017 at 01:49 PM.
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Old December 22, 2017, 09:00 PM   #10
DMiller23
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Thanks for all the help guys!! Went back to the range that I origanly shot the above group at. After going to my personal range last weekend and finding a good load to work with in this rifle. (Shooting at 100 on level ground) I just set a zero at 100 with the loads for the time being. Today, at the longer range that I had the issue with to begin with, shot at 200 to get a true 200 yard zero. Same elevation change as before and all factors and variables the same except the change from factory to hand loads. Shot a 5 shot 1.22 group being 1.75 inches low to center of group. (Still have some adjusting to do in the headspace and bullet jump) zeroed at 200 and confirmed with 3 shots. Moved back up to 100 and shot another 5 shot group. Center of group being .78 inches high. The change of performance in the hand loads vs factory loads seem to make up the difference in the equation. Getting close to having this new Howa dialed in and ready to hunt. Just to add, this is my first Howa rifle and I am absolutely in love with this rifle and scope set up. I have shot vx3's for years off of remington 700's but the feel of this rifle is unquestionable the best hunting rifle I have ever shot. Again guy, thanks for the help and the link to the ballistics calculator.
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Old December 22, 2017, 09:36 PM   #11
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Spelling and grammar count!
Count? uh, no that's math if your counting

Oh come on that's funny.

everything I own is on perfect zero, twice every shot.
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Old December 23, 2017, 03:26 PM   #12
DMiller23
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Theirs always that one guy
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