Sighting in on flat vs hill

[deckhandmike]

[Spaffo]

I would think shooting horizontally would be more accurate, but at 200 yards, it probably is negligible.

[NapalmCheese]

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?

Crazy math for what? About as crazy as you'd have to get is c=sqrt(a*a+b*b)

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.

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.

[sigstroker]

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.

[ar15barrels]

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...

Angle Fire Table	
2.5º	1.00
5º	0.99
7.5º	0.99
10º	0.98
12.5º	0.97
15º	0.96
17.5º	0.95
20º	0.94
22.5º	0.93
25º	0.91
27.5º	0.89
30º	0.87
32.5º	0.85
35º	0.82
37.5º	0.80
40º	0.77
42.5º	0.74
45º	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.

[JackEllis]

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.

[XVIga_Rob]

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.

[estrom]

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.

[smoothy8500]

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.

[RandyD]

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.

[newbutold]

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.

[ar15barrels]

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.

[deckhandmike]

Looks like I’ll just find a flat spot. Might as well go for a hike. Thanks.

[NapalmCheese]

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.

[Fjold]

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.