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Centerfire Rifles - Manually Operated Lever action, bolt action or other non gas operated centerfire rifles.

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  #1  
Old 12-04-2019, 10:44 PM
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Default Sighting in on flat vs hill

I got to sight in some rifles and my flat range is only to a 100 yards and I need to sight in at 200 yards. The 200 yard zero is non negotiable. I donít want to do crazy math. Should I just find a flat 200 yard spot which might be a PITA or will off level work. Both spots have a fairly significant rise. I have a feeling Iíll need a level spot but who knows. Thatís why Iím asking. I have a rangefinder with elevation calculation but I donít really trust it for a perfect zero.
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Old 12-04-2019, 11:14 PM
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I would think shooting horizontally would be more accurate, but at 200 yards, it probably is negligible.
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Old 12-04-2019, 11:44 PM
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Quote:
Originally Posted by deckhandmike View Post
I got to sight in some rifles and my flat range is only to a 100 yards and I need to sight in at 200 yards.
I get that you want to be zeroed at 200 yards, but is it really so bad if you're a half inch low or high at 200?

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Originally Posted by deckhandmike View Post
The 200 yard zero is non negotiable. I donít want to do crazy math.
Crazy math for what? About as crazy as you'd have to get is c=sqrt(a*a+b*b)

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Originally Posted by deckhandmike View Post
Should I just find a flat 200 yard spot which might be a PITA or will off level work.
Seems like you won't be confident if you don't, so yeah you probably should.

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Originally Posted by deckhandmike View Post
Both spots have a fairly significant rise. I have a feeling Iíll need a level spot but who knows. Thatís why Iím asking. I have a rangefinder with elevation calculation but I donít really trust it for a perfect zero.
You don't trust the math and you don't trust your equipment (at least not the rangefinder). Do yourself a favor and just find a flat 200 yard range.
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Old 12-05-2019, 12:55 AM
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Find a free online ballistic calculator, enter the parameters, and it will show the ballistic curve. Tell it you want to zero at 200, look up the trajectory at 100 to see where it should be at that range, and sight in to be X inches high at your 100 yard range.

Chances are it will be a little bit off because you won't have exact velocity data, etc, but it should be really close.
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Old 12-05-2019, 1:15 AM
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Quote:
Originally Posted by deckhandmike View Post
I got to sight in some rifles and my flat range is only to a 100 yards and I need to sight in at 200 yards. The 200 yard zero is non negotiable. I don’t want to do crazy math. Should I just find a flat 200 yard spot which might be a PITA or will off level work. Both spots have a fairly significant rise. I have a feeling I’ll need a level spot but who knows. That’s why I’m asking. I have a rangefinder with elevation calculation but I don’t really trust it for a perfect zero.
How much angle?
Adjust your angled zero back to level based on the angle correction required...

Code:
Angle Fire Table	
2.5ļ	1.00
5ļ	0.99
7.5ļ	0.99
10ļ	0.98
12.5ļ	0.97
15ļ	0.96
17.5ļ	0.95
20ļ	0.94
22.5ļ	0.93
25ļ	0.91
27.5ļ	0.89
30ļ	0.87
32.5ļ	0.85
35ļ	0.82
37.5ļ	0.80
40ļ	0.77
42.5ļ	0.74
45ļ	0.70
The table gives you angle correction percentage.
Zero at 200.
Then shoot at 100.
Calc what your 100-200 dope should be and then figure out how far off you are and adjust the percentage from above to your 200yd zero to get yourself a level 200yd zero.

The other way to do it is to zero at 100, figure out what your 200yd dope should be and dial that correction.
Then shoot at 200 and see how high it is.
Then correct your 200yd zero by that amount the opposite way so that your 200yd shots on a slope end up high like they should.

A good ballistic calculator will tell you how much to change your zero based on the angle of your zero.
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Last edited by ar15barrels; 12-05-2019 at 1:19 AM..
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  #6  
Old 12-05-2019, 7:25 AM
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Most of what I've learned about hunting comes from a friend who's been at it for 50 years. His rule of thumb for getting a 200 yard zero using a 100 yard range is simple. The POI at 100 yards should be to inches above the bull. If you run through some examples on a ballistic calculator (gundata.org has one) you'll see that his rule works well enough for centerfire hunting calibers.

When Divernhunter weighs in here he's going to say 2.5 inches high. Either one is close enough for hunting rifles. If you're shooting precision, things might be different but I doubt it.
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Old 12-05-2019, 8:14 AM
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The math has already been done. Use a ballistic calculator that matches your load, or at least as close as possible. Using the 100 yard range, zero accordingly. Confirm @ 200 if possible.
* If shooting copper, make sure your calculator is configured for it.
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Old 12-05-2019, 8:26 AM
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Originally Posted by XVIga_Rob View Post
The math has already been done. Use a ballistic calculator that matches your load, or at least as close as possible. Using the 100 yard range, zero accordingly. Confirm @ 200 if possible.
* If shooting copper, make sure your calculator is configured for it.
This. You're making it more complicated than it needs to be. The 100 yard range will work.
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Old 12-05-2019, 8:54 AM
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Originally Posted by JackEllis View Post
When Divernhunter weighs in here he's going to say 2.5 inches high. Either one is close enough for hunting rifles. If you're shooting precision, things might be different but I doubt it.
Funny how almost every rifle shoots the same 2MOA "UP" for 200yds....No need to re-invent the wheel.
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Old 12-05-2019, 9:50 AM
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Napalmcheese, gave you your best answer. If your confidence depends upon you sighting in on a flat 200 yard range, then do it.

Your your bullet weight, bullet coefficient and muzzle velocity , and the degree of the hill's incline, will be the factors that affect how far off your point of aim is from your point of impact. At 200 yards, I doubt that an incline will cause anything more than .5" difference in the point of aim and the point of impact.
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Old 12-05-2019, 10:45 AM
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I sight in on the level @ 100yds. I've made one-shot kills on animals way uphill and way downhill with my .270 and 7mag.

Take your rifle for a hike and pick out a target at the limit of your comfort range and see if you can hit it.
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Old 12-05-2019, 10:45 AM
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At 200 yards, I doubt that an incline will cause anything more than .5" difference in the point of aim and the point of impact.
A 90 degree incline eliminates all effects of gravity on bullet drop from line of departure.
This usually causes a 100yd zero of an optical sight to be off by more than 3moa.
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Old 12-05-2019, 11:44 AM
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Looks like I’ll just find a flat spot. Might as well go for a hike. Thanks.
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Old 12-05-2019, 12:27 PM
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Quote:
Originally Posted by RandyD View Post
Napalmcheese, gave you your best answer. If your confidence depends upon you sighting in on a flat 200 yard range, then do it.

Your your bullet weight, bullet coefficient and muzzle velocity , and the degree of the hill's incline, will be the factors that affect how far off your point of aim is from your point of impact. At 200 yards, I doubt that an incline will cause anything more than .5" difference in the point of aim and the point of impact.
The adjunct is: Don't sweat it too much. Sight in 2.5-2.75 inches high at 100 yards for a point blank range of around 250-300 yards and don't worry what that actual zero of your rifle is unless you plan on holding over for targets past your MPBR.

The lemma: I referenced c=sqrt(a*a+b*b) because when you're shooting uphill or downhill the effects of gravity pretty well only matter to the horizontal component of your range. So, if you can do geometry and/or trig you can figure out your horizontal component and calculate your drop using that component instead of the hypotenuse (which is the actual, lasered or whatever, uncorreted range to uphill or downhill target).

Anyway, you don't say what the application or cartridge is but; if this is for hunting I'd just sight in 2.5-2.75 inches high at 100 yards and hold in the 'pocket' just above the elbow and behind the shoulder out to 250 yards. That'll hold true for about anything from .30-30 (with gummy bullets) to .30-378 wby.
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Old 12-05-2019, 4:05 PM
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Measure the angle of the hill:

If it's 20 degrees. the horizontal distance will be .94 (cosign of 20) of the visual (laser) distance. Set your target at a lasered 212.765 yards to get a 200 yard zero.

At 30 degrees the cosign is .82 so set your target at a lasered 243.9 yards.
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Old 12-05-2019, 4:28 PM
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Were yall this good at match in high school? I sure wasn't.
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Old 12-05-2019, 4:51 PM
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Were yall this good at match in high school? I sure wasn't.
I went to school in Califonia. They didn't let us shoot guns.
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Old 12-05-2019, 4:52 PM
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Use the ballistic chart on the ammo box and check for variance.

Best to sart with basics on the level.

25 yards then 100 yards then check the angles.
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Old 12-05-2019, 4:55 PM
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Quote:
Originally Posted by Fjold View Post
Measure the angle of the hill:

If it's 20 degrees. the horizontal distance will be .94 (cosign of 20) of the visual (laser) distance. Set your target at a lasered 212.765 yards to get a 200 yard zero.

At 30 degrees the cosign is .82 so set your target at a lasered 243.9 yards.
I might cosign a loan. I've also found the cosine of angles.

You are correct with your procedure, though.
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Old 12-05-2019, 4:55 PM
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Originally Posted by ar15barrels View Post
A 90 degree incline eliminates all effects of gravity on bullet drop from line of departure.
This usually causes a 100yd zero of an optical sight to be off by more than 3moa.


won't it cone back and hit you on the head?
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Old 12-05-2019, 4:58 PM
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find a 100yrd target that marks a 200yrd zero.

similar to this
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Old 12-05-2019, 5:00 PM
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won't it cone back and hit you on the head?
And, neglecting air resistance, the bullet will hit your noggin at the same velocity it had when it left the muzzle.

That's going to leave a mark.
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Old 12-05-2019, 5:18 PM
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It’s just important to me to be dead on since this will be for a hunting rifle and I might, just might be willing to stretch it out over 400 yards or so. I can shoot fine but I don’t want to wound anything needlessly over poor planning. I will be shooting .300 win mag. And yes, I’ll go find a flat spot so I’m confident of my zero. Thanks for the replies. I was just being lazy and figured it couldn’t hurt to ask and judging from the range of responses maybe a few others learned something too.
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Old 12-05-2019, 6:14 PM
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won't it cone back and hit you on the head?
Only if you are shooting UP in vacuum.
When shooting up in normal atmosphere, the atmosphere will act on the bullet and it will not come back to where it left from.
When shooting down, gravity keeps the bullet from coming back up at you.
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Old 12-05-2019, 6:18 PM
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Originally Posted by deckhandmike View Post
Itís just important to me to be dead on since this will be for a hunting rifle and I might, just might be willing to stretch it out over 400 yards or so. I can shoot fine but I donít want to wound anything needlessly over poor planning. I will be shooting .300 win mag. And yes, Iíll go find a flat spot so Iím confident of my zero. Thanks for the replies. I was just being lazy and figured it couldnít hurt to ask and judging from the range of responses maybe a few others learned something too.
What's your definition of "dead on" in moa?

Make sure you get your game to be level to you as well because uphill or downhill is going to effect the bullet when you are trying to be "dead on" the game too.

Just plan to only shoot your game at the same weather conditions and inclination as you set your zero and you are all good.
Otherwise, atmosphere is gonna atmosphere you "dead off" the bullet from your aiming point.
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Old 12-05-2019, 6:32 PM
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Were yall this good at match in high school? I sure wasn't.
That's jr. high math.
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Old 12-05-2019, 7:03 PM
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Originally Posted by ar15barrels View Post
What's your definition of "dead on" in moa?

Make sure you get your game to be level to you as well because uphill or downhill is going to effect the bullet when you are trying to be "dead on" the game too.

Just plan to only shoot your game at the same weather conditions and inclination as you set your zero and you are all good.
Otherwise, atmosphere is gonna atmosphere you "dead off" the bullet from your aiming point.
Well obviously thatís the plan. Way easier to drag it back to the truck when everything is level.
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Old 12-05-2019, 7:17 PM
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Well obviously thatís the plan. Way easier to drag it back to the truck when everything is level.


But it's even easier if you park at the bottom of a hill and shoot the critter at the top of the hill so it just rolls down to the truck.
That's how we shoot pigs.
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Old 12-06-2019, 8:32 AM
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Confucius say Man who wants to shoot precusely at 400yds but has no chrono and cant use ballistics calc often misses.

At 400 yds for high precision shooting chrono and ballistic calc only is for reference. Shoot at the various distances and get your dope from actual shooting.
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Old 12-06-2019, 9:18 AM
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With a new rifle/scope combination, I start at 25yds from a bench.
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