How accurate must the 100 yard zero be to make hits out to 1000 yards? Is it plus or minus 1 yard, 1 foot, 6 inches? Where to I measure from? I have read from the end of the barrel and other have said from the turrets of the scope.
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How accurate must the zero range be?
- Thread starter AR10ShooterinNC
- Start date
not an expert, but i would probably base your dope on an aggregate of known results from your gun at various distances.
does that zero give you good dope for 300 or 500 yards?
i adjust ballistics based on what happens in the real world with my rifle and particular ammo.
does that zero give you good dope for 300 or 500 yards?
i adjust ballistics based on what happens in the real world with my rifle and particular ammo.
If you are checking the accuracy of the adjustments of your scope turrets, you should know your distance from turrets to target as close as possible. Get a 300ft tape measure from Amazon for $20. My Bushnell Nitro 1800 only has +/- 1yd accuracy. Even the much-lauded Leica CRF is only good to 1/2m at <200m. Even my Leica Disto A3 is only good to 100yds but is accurate to +/- 1/16". That is what I use for checking distance to target.
Also remember 1moa = 1.047" at 100yds, not 1" at 100yds. It matters.
If you're setting zero at "100yds" and you're at 105 yds, you're 5% off and it will affect your trajectory in your calculator.
Your distance needs to be dead nuts on for tracking tests otherwise the numbers are useless. Distance is assumed (or defined as a finite number) in those calculations to check proper tracking per unit in the scope. I remember reading that at one of the SH training classes they used a laser RF that was off enough that they had issues resolving data on a tracking test.
As far as rifle zero is concerned I would argue an exact distance is not as imperative. The rate at which bullet drop occurs is smallest at the beginning of the trajectory. The idea of a 100yrd zero is that at that distance the impact of environmental factors - wind/DA etc is arguably not needed to be taken into account. If your zero is off let’s say 2” at 100, that 2” error will carry throughout your trajectory but will not be magnified along its path. A general ballistic solution for a 175MK with a MV of 2600fps shows the same vertical trajectory from 90-101 yards meaning if you zero at any point in that distance your zero is “correct”.
Edit - I could be wrong about this, just my understanding. Hopefully those that are smarter than me chime in.
As far as rifle zero is concerned I would argue an exact distance is not as imperative. The rate at which bullet drop occurs is smallest at the beginning of the trajectory. The idea of a 100yrd zero is that at that distance the impact of environmental factors - wind/DA etc is arguably not needed to be taken into account. If your zero is off let’s say 2” at 100, that 2” error will carry throughout your trajectory but will not be magnified along its path. A general ballistic solution for a 175MK with a MV of 2600fps shows the same vertical trajectory from 90-101 yards meaning if you zero at any point in that distance your zero is “correct”.
Edit - I could be wrong about this, just my understanding. Hopefully those that are smarter than me chime in.
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I have no idea why you say absolute wind deflection does not increase w range as it’s an angle just like elev, right?
You’ve got a ballistic app...run the numbers with a 100 yard zero and a 105 yard zero; you’ll be surprised. Now the distance for a scope tracking test measured to your turrets is another matter as are the inputs for your zero height and windage offset
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you'll get dope that is a little under what it should be (if height over bore, velocity and bc are all exactly right).
I am new to this game but going to attempt to answer.
You need to know the ballistics of said round and firearm combo. Bullets are affected by gravity and start falling as soon as they leaves the barrel. The faster they travel the less they fall for a given distance.
For instance a .308 falls about 5ft at @500 yards. And over 30feet at @1000.
There are different weight and different aerodynamic drag, for different .308 rounds which are speed dependent ( g1 ballistic coefficient ) but that is ball park performance. The muzzle velocity of .308 is around 2600fps(dependent on gun and round combo), by 1000 yards it has slowed to around 1100 to 1200 fps.
The speed of sound is around 1125fps. When bullets pass below mach one(speed of sound) the shock wave dissipates and changes the center of pressure. This can and generally does cause a loss of stability.
Wind can also affect elevation and windage... wind is harder to predict and the biggest challenge in long rang shooting. Gravity is pretty constant, wind is not.
These are all things you need to consider.
So to answer what I think you were tryin to ask. How far off a 100 yard zero do you need to be to hit at 1000?
Answer... It depends. What Tools are u using, what are the conditions in which u are doing it.
What type of reticle does your scope have. Do you understand how to use a reticle and what type of adjustments it uses(moa/mil radians). You can compensate off any zero. Point of aim and point of impact. If you shoot and your impact is 3mil down and 2 left. You can use the reticle to compensate.
The difference between 95 and 100 yards is negligible and your ability to hold the gun straight combined with wind will likely have a greater affect on your consistency. This is amplified by distance. Especially out over a half mile.
The app I'm using is BallisticARC for iOS, my rifle is an AR-15, 20" barrel. My current load is 69 gr SMK, muzzle velocity is 2925 fps, using a chrono. Looking to hit an IPSIC torso plate 600 to 1000 yards. My scope is mil adjustments, reticle is mil dots, yes I understand how the adjustments work and how to hold over if needed. I hold left or right or wind, and dial for elevation.
The range I'm a member of and closest to my home only goes out to 400 yards (they are working on going to 1000 yards). When I was last at the 100 yard range, there was a guy that had laser range finder, he was saying that the range from firing line to the targets was in reality 97 yards.
Throwing it out there that Strelok says if you zero at 100 with that bullet and velocity, your 600 dope = 4.6mil, 800 = 8.4 and 1000 = 13.9. After 700, you are subsonic (assuming an 80F zero temperature and all other atmospherics are the same). For a 97yd zero, the data is the same. If you are looking to reach past 700yds consistently with that rifle, I suggest you look at single-loading 90SMKs at about 2600 if your barrel is a 7-twist or faster. Even the 77TMK at 2750fps will only get you to 850 for transonic. I had a John Holliger PacNor 6.5 twist in my 20" service rifle about 20 years ago that would shoot 90gr JLKs at about 2575-2600 with a 4895 load and CCI450s. It shot OK (185-190/200) at 1000, better (195-clean) at 600.
The amount of difference from 97 to 100 yard zero is negligible on your calculations trying to push 5.56 out that far with a semi auto. The atmosphere and your technique will make more of a difference than 3 yards at a 100 yard zero in a ballistics calculator.
What I personally would do is work your way out. Start at 100 then 200, 250 and so on....
Find a spotter at the range that knows what they are doing and have them help you with your dope and holds. Write down what you are doing and use it as a reference. Things like elevation and windage dope, wind speed and direction, air pressure, temperature, humidity etc.
I literally just went through this with in the last month, transitioning from a 100 yard being the furthest I have shot, to a range that is almost 1100 yards.
It takes alot of info to get a ballistics calculator to be accurate 1st shot type stuff, I would not expect that. Its more of a ballpark estimate that you must then compensate.
The combo you are wanting to use goes subsonic around 7-800. And is dropping pretty fast. By 800 you are subsonic and 240 inches off your 100 yard zero in elevation and u will be adding around 8 to 10mil(80 to 100 clicks)elevation to get there, in theroy. Wind will be pushing that light round all around, a 10 mph wind could push you 100” off target at 800. That sounds like a tough shot but not impossible.
That being said I have personally never shot a 5.56 out that far or used the Ballistics calculator you mentioned
What I personally would do is work your way out. Start at 100 then 200, 250 and so on....
Find a spotter at the range that knows what they are doing and have them help you with your dope and holds. Write down what you are doing and use it as a reference. Things like elevation and windage dope, wind speed and direction, air pressure, temperature, humidity etc.
I literally just went through this with in the last month, transitioning from a 100 yard being the furthest I have shot, to a range that is almost 1100 yards.
It takes alot of info to get a ballistics calculator to be accurate 1st shot type stuff, I would not expect that. Its more of a ballpark estimate that you must then compensate.
The combo you are wanting to use goes subsonic around 7-800. And is dropping pretty fast. By 800 you are subsonic and 240 inches off your 100 yard zero in elevation and u will be adding around 8 to 10mil(80 to 100 clicks)elevation to get there, in theroy. Wind will be pushing that light round all around, a 10 mph wind could push you 100” off target at 800. That sounds like a tough shot but not impossible.
That being said I have personally never shot a 5.56 out that far or used the Ballistics calculator you mentioned
To answer your original question, you do not need to be at exactly 100 yards to zero, or really even close. I just ran my ballistic app in 5-yard increments, and for a 100-yard zero, it gives me NO CHANGE in elevation from 75-125 yards, and only .1 mil from 60-155 yards. So if you are zeroing at 100 +/- 10 yards, you will be more than fine.
As long as you’re not trying to do scope tracking then your margin of error is pretty decent. Doesn’t have to be right at 100y.
If you put 100y in your ballistic app and the distance is really 107y the difference is so minuscule it won’t matter.
If you put 100y in your ballistic app and the distance is really 107y the difference is so minuscule it won’t matter.
And there is the surprise I mentioned...so little you could not shoot the difference.
In Meters. Same gun, same everything, different zero range. 94m, 100m, 106m. You decide.
