coriolis

Last week we posted an Ammoland article about maximum point blank range. The article touched on — but didn’t explain — some topics related to long range shooting. Among them: the Coriolis effect . . .

As far as shooting is concerned, the Coriolis effect is the Earth’s rotation causing the target to move away from the bullet as it travels. So you have to make adjustments, but do you compensate by aiming up, left, down, right of the target? Let’s find out . . .

First, the results of Coriolis effect:

• If you’re in the Northern Hemisphere shooting North or South, you’ll hit right of your target.
• If you’re in the Southern Hemisphere shooting North or South, you’ll hit left of your target.
• If you’re in either Hemisphere shooting East, you’ll hit high.
• If you’re shooting West, you’ll hit low.

Shooting North or South:

Perhaps the hardest fact to wrap one’s head around: when we’re shooting in the U.S. of A. the Coriolis effect causes a miss to the right, whether we’re shooting in a northerly or southerly direction.

Envision the following scenario, then we’ll scale it up to long range shooting over the moving Earth . . .

You’re in a car driving 60 mph down the highway. There’s a stationary target 200 yards away in a field directly off the driver side of the car. If you shoot out of the car at the target [ED: don’t shoot from cars], you’ll miss to the right of the target. That’s because your bullet was in your gun, in your car, going 60 mph in the car’s direction when it was fired. It kept moving in that direction even as it simultaneously flew away from the car.

Likewise, if you stand at this target and you fire directly at the driver side of the moving car [ED: don’t shoot at cars], you’ll also miss to the right. Your shot will have gone straight, but the car kept moving and was no longer in that spot when the bullet arrived.

Conversely, if you’re shooting at a target off the passenger side of the same car going the same direction, you’d miss to the left, whether you’re shooting from car-to-target or from target-to-car.

In this metaphor, the car is the Earth’s equator. It’s moving East at 1,037 miles per hour. The Equator is the fastest-moving line of latitude on Earth because it’s the largest in diameter and, therefore, farthest from the Earth’s rotational axis.

For example, at 45 degrees North (halfway between the Equator and the North Pole, a.k.a. along Montana’s southern border) you’re only moving about 733 mph. If you’re shooting at “the car” (the Equator), it’s moving East faster than you are and you miss to the right. If you’re “the car” and shooting at Montana, it’s moving East slower than you are and you miss to the right.

Likewise, if you’re shooting south of the Equator, whether South from “the car” or North up towards it, you miss left/left. FYI, in the off chance you’re shooting across the Equator from one Hemisphere into the other at a target equidistant from the Equator as you, you’ll be spot-on.

If the car thing doesn’t make sense, another example — though it doesn’t scale up to match what’s truly going on in long range shooting on Earth — is that of a playground merry-go-round (roundabout).

You and a friend are on the merry-go-round and you’re sitting across from each other on opposite sides, facing inwards. It’s spinning fast, and you throw a ball across to your friend. What happens?

If the roundabout is spinning counter-clockwise, you’ll miss to the right. So will your friend. It doesn’t matter who’s throwing the ball across, the ball will miss to the right of the target.

This is the same effect as shooting North or South if you’re in the Northern hemisphere. If the roundabout is spinning clockwise, you’ll both miss to the left. This is the same effect as shooting North or South if you’re in the Southern hemisphere.

Shooting East or West:

If you’re shooting East or West, regardless of hemisphere, Coriolis effect makes you miss high or low, as the earth is either effectively dropping below your bullet (shooting East) or coming up at it (shooting West).

The Earth is spinning to the East fast enough to complete one rotation every day (what a coincidence!). As mentioned, on the equator, that’s 1,037 miles per hour and it’s slower and slower as you approach the poles, until eventually you’re at a pole and you aren’t moving (discounting motion through space and time) at all, but just spinning in place (and you can only shoot either due South or due North).

Had you zeroed your rifle while shooting North or South, if you take a shot due East you’ll hit high and due West you’ll hit low. While most of us focus on the North/South effects of Coriolis causing a “windage” drift, the East/West effects on elevation are typically even greater.

How Much Does it Matter?

In most of these cases we’re talking about some 2 to 6 inches at 1,000 yards depending on caliber and, particularly in the case of East/West shooting, latitude.

Examples with .308 Win shooting 168 grain Federal Gold Medal Match:

• North/South at 1,000 yards: about 3 inches right if in Northern Hemisphere, left if in Southern
• East/West at 1,000 yards while here in Austin: 4 inches high if shooting East, low if West (at the equator it would be 4.6 inches)

• North/South at 1,500 yards: 8.7 inches right if in Northern Hemisphere, left if in Southern
• East/West at 1,500 yards while here in Austin: 13.5 inches high if shooting East, low if West

Add spin drift — the bullet’s drift off course due to the right- or left-hand rotation on it imparted by the rifling (a typical .308 bullet is spinning something like 188,000 rpm) — to the Coriolis effect and you’re easily missing targets even in dead calm conditions.

For example, you’re looking at 39.2 inches of spin drift at 1,500 yards with the .308 load above. In most rifles it’s drift to the right, as most rifles have right-hand twist rifling. Add in Coriolis and you’re now 47.9 inches right of target and you’ve just missed by a long shot.

The Math

Your ballistic app will take care of it, don’t worry. But you’ll want to know your latitude and your azimuth (the direction you’re shooting, in degrees from true North). In many cases, the GPS in your phone can provide that information to your ballistic app. “You should end the Coriolis article with something funny.” — Robert

 

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89 COMMENTS

  1. The wind’s gettin’ a bit choppy. You can compensate for it, or you can wait it out, but he might leave before it dies down. It’s your call. Remember what I’ve taught you. Keep in mind variable humidity and wind speed along the bullet’s flight path. At this distance you’ll also have to take the Coriolis Effect into account.

    • Is that from Shooter?

      (FYI the effects of humidity are very minor. Just use station pressure and you’re GTG, leaving humidity in your program at 50% basically all the time and ignoring it.)

      • Call of Duty: Modern Warfare, too bad this is from the same series that regularly pimps random snowflake guns in the hands of what are supposed to be actual military units.

  2. None of this sounds like it is going to be useful to beginners. Need to get some basics straight first, then one can wrap themselves around this stuff later.

    Please don’t confuse the newbies.

    • Kinda what I was thinking, Mama.
      If someone has graduated to a skill level where the Coriolis Effect is something they need to be concerned with – they have long since stopped being a beginner.
      Interesting physics anyway, fun for academic reasons alone.
      🤠

    • Mama,
      At some point, every rifle enthusiast grows bored at ringing steel plates at 300 yards and decides to try a new challenge. He hops on his 4-wheeler and drags a target out to 1,000 yards, and drops a few milk jugs out there just for kicks.

      At this point, even if he is an experienced rifle shooter, he is a long range shooting BEGINNER.

  3. ‘…on the equator, that’s 1,037 miles per hour…’

    Hmm… so 1037mph just happens to be 1520fps, which just happens to be the velocity Double Tap claims I get out of their 158gr. .357s out of my 6″ GP 100. So, if we are both standing on the equator and you are to the west of me and I shoot you, the bullet will actually stand still while you rush to the bullet at 1520fps. On the other hand, if you are to the east the bullet actually accelerates to 3040fps, but you’re rushing away at 1520fps, so it will still catch up with you with pretty similar results. However, the earths gravitational pull is constant regardless of spin, so shooting east results in 3040fps of centrifugal force working against gravity, whereas shooting west results in no centrifugal force.

    Once you think about it makes sense.

    • That’s an interesting way to explain why you hit high shooting E and low shooting W. Haven’t heard that one before but it’s fun and it makes some logical sense. Whether it explains some of the real life end results or all of them or what I don’t know, but as far as shooting is concerned the true “why” from a physics perspective is nice to know but not as critical as remembering the “what” (E hit high, W hit low).

      • For the record, I figgerd that out all by myself.

        I would think that’s the whole of the principal at work her for E vs W. If you tie a string to a ball and spin it around your head, the faster you spin it the harder it pulls on the string. If you were in outer space hovering over the same spot, at some point the bullet would reach escape velocity (from orbit) when shot to the east but would fall right back to earth when shot west. Obviously from the ground, escape velocity is much higher than any rifle bullet will go regardless of which direction you fire it. Maybe there’s other forces at work here that I don’t fully comprehend but a difference of +/- 1000mph would seem to be enough to lift or drop a bullet 4 inches after 1000 yards.

        BTW, the why is ultimately more important than the what, because if you know the why you’ll figure out the what. For instance, if you only knew the what, you’d know that you have to hold left when shooting north or south. But if you didn’t know the why, if you went to the southern hemisphere you’d hold left and wonder why your bullet hit 8 feet off.

    • For a more concise and easy to understand explanation, please read Einstein’s “Theory of Relativity”.

      • Do you mean that there’s no such thing as centrifugal force or that the earth isn’t spinning on it’s axis? Is the earth flat?!?

        • Actually, there isn’t such a thing as centrifugal force. It’s imaginary.

          Really. There’s no force that tries to fling something off the face of the Earth. It’s just an object’s inertia and desire to travel in a straight line. It’s centripetal force that’s real, and is what pulls against an object to cause it to deviate from the straight line it wants to travel on. The imaginary outwards force that helps us visualize what would happen without the actual centripetal force is called centrifugal force.

        • Well, reactive centrifugal force does exist. If an object has sufficient inertia it will go in a straight line and therefore appear to be flung from the earth. Just not directly opposed to the centripetal force that gravity imposes on it. Spin a ball on a string and the faster you spin it the more tension is applied to the string, so if you’re not splitting hairs centrifugal force does, in a sense, exist. The ball resists the centripetal force the string imposes on it, but the force is not applied directly opposite to the axis. Let the string go and you’ll see that in the absence of centripetal force the laws of inertia go unopposed.

          • It’s my understanding that the string is applying centripetal force? The very real force pulling inwards against the imagined opposite “centrifugal force,” but in reality it’s just the force necessary to constantly change the object’s velocity and there is no actual opposite outwards force since the ball doesn’t want to go outwards, it wants to go straight off at a tangent.

        • Yes, the string exerts the centripetal force. Centrifugal force only doesn’t exist in the sense that it doesn’t directly oppose the centripetal force. Centrifugal effect would probably be a more appropriate name, since the real force in action is just inertia and it’s acting at a right angle to the radius. But the effective result is an outward force. If you ride the silly silo, the wall behind you becomes the centripetal force (now a pushing force rather than a pulling force). When the floor drops out from below your feet, your inertia makes you want to continue traveling left of right, but there’s still enough outward force to keep you pinned against the wall, defying gravity as it would appear.

          But then high school physics was quite a while ago.

    • So what your saying is if I shoot a bad guy that’s coming at me from the east with a shotgun, he will get knocked off his feet… At the equator with slugs anyway.

      • Only in a vacuum. On earth it’s the 1000mph wind that knocks him off his feet.

  4. Me thinks there is a small piece missing here. At the equator the Earth rotation rate is 1,037.54 miles/hour. That equates to 1,521.728 feet/sec. Not 4 inches. However the bullet, whilst still in the chamber, is also moving at the same rate in the same direction as the target. So it appears to me that the offset is a function of the constantly moving target (due to Earth rotation) with respect to the decreasing (Earth) rotation rate of the bullet whilst in flight. Is that correct? And how does one calculate how much the bullet slows it (Earth) rotation rate per second of flight?

    • The bullet’s spin from the rifling isn’t a related factor here. If you could launch an arrow or a ball bearing fast enough to go extreme long distance you’d see the same Coriolis effects even if those things didn’t spin at all.

      If you’re shooting N or S within the N or S Hemisphere, you aren’t moving the same rate as the target. This is the cause of the right or left “drift.”

      If you’re shooting E or W, the explanation for hitting high or low that I’ve heard the most has to do with the curve of the Earth. The target is either getting lower relative to the bullet and you hit high because of it, or the target is coming upwards and you hit low because of it.

  5. That was a pretty funny ending.

    Now do pinwheels.

    Oh, and thanks for fixing the previous article.

  6. This principle alone completely disproves flat earth theory. Let alone the rotation, but the actual curvature of the earth. It’s pretty fascinating to understand these things when you’re shooting far enough that they have an effect.

    • Though in that image I made, if the flat earthers believe the planet spins like a merry-go-round on an axis at the middle of Africa, N/S shooting would still cause a left/right drift but it would be reversed, since you’d be moving faster at the outside and slower toward the middle.

    • Jon in CO,

      Never underestimate the ability of someone to invent whatever factors/forces they need to support their “hypothesis”.

  8. “In most of these cases we’re talking about some 2 to 6 inches at 1,000 yards …”

    According to my math, the difference in velocity of two points separated 1,000 yards north-south on our Earth’s surface would only cause your bullet to hit about 1.34 inches left or right from expected point of impact. What other effect makes up the difference and produces “2 to 6 inches”?

    —

    Here is my simple math:

    We can interpolate between the data points that Jeremy S. provided to estimate the difference of east-west velocity for two points that are 1,000 yards apart north-south. One degree of latitude is about 69 miles or 121,440 yards. Therefore the difference in east-west velocity, in m.p.h per yard of north/south separation, is about:
    (1,037 – 733) mph / (45 degrees latitude * 121,440 yards per degree latitude)
    = 0.00005563 mph / yard of north-south separation

    Thus, if you and the target are 1,000 yards apart north-south, your difference in east-west velocity is about 0.05563 mph. Now we have to translate that to feet per second to see how many feet east-west the bullet moves during the transit time to fly 1,000 yards north-south:
    0.05563 (miles / hour) * (5280 feet / mile) * (1 hour / 3600 seconds) = 0.08159 feet per second.

    Assuming that a typical rifle bullet has an average velocity of roughly 2,200 feet per second during its 1,000 yard flight to its target, the bullet would be airborne for about 1,000 yards * (3 feet / yard) / 2,200 feet per second = 1.364 seconds. Thus, the bullet would “drift” about 0.08159 feet per second * 1.364 seconds = 0.1112 feet which equals 1.34 inches.

    • Okay, I found the error in my math: using the equator and 45 degrees latitude to estimate the east-west velocity difference of points that are separated north-south is not accurate.

      In my original calculation: I estimated that the east-west velocity difference of two points that were 1,000 yards apart north-south was about 0.05563 mph. It it is actually about 0.0958 mph. That means a typical rifle bullet would hit about 2.3 inches left/right of the point of aim if you and the target are 1,000 yards apart and you are at 40 degrees latitude.

    • The .308 load mentioned, your venerable 168 grain FGMM .308, leaves the muzzle at about 2,610 fps but, at 1,000 yards, it’s only doing 1,070 fps. It takes 1.856 seconds to get to the target. I’m not sure if the fact that it spends a lot more time in its final 1/3 of its trip than in its first 1/3 matters in this case.

      Also, “In most of these cases we’re talking 2 to 6 inches” is speaking of any Coriolis effect, not only N/S effect. Since E/W effect is larger, the low end (2″) of that estimate is geared towards N/S shots and the high end (6″) is geared towards E/W. And as we see in the practical examples with the .308 load, it’s like 3″ and 4.6″ so those numbers will increase with projectiles that spend more time in flight and decrease with projectiles that spend less, so I said “2 to 6” to cover most cases.

      • Jeremy,

        Yeah, I think your 2 to 6 inches is pretty accurate. Between my velocity factor being too low and flight times being a bit longer, I can easily see a shot drifting between 2 and 6 inches depending on your latitude, muzzle velocity, and downrange velocity.

        Thank you for the article. It is an important reminder for anyone who wants to shoot out to 1,000 yards and beyond.

        • Jeremy, if you have multiple spotting rounds and a large target, 1,000 yards isn’t that far.
          Now try the torso of a IDPA/ at 1,000 yards with one shot on a cold bore. By yourself.
          Whole different world.

        • I just said that so I could make the “pull the trigger harder” joke haha

          Farthest I’ve hit an IPSC silhouette is 1,960 yards. Not on the first try. Honestly I’m not entirely sure what the longest first-shot cold bore hit I’ve made is. I think in every scenario where I’ve plunked down behind a long range rifle I’ve started at a more achievable (due primarily to wind call) distance and then worked my way out once I had the wind figured out. I know I took that Gunwerks 6mm Creedmoor rifle out of the box and hit at 600 first shot. I took an Alamo Precision Rifles rifle and shot at a 24×24 steel plate at something around 1,350 yards and, first shot through it, was off the side of the target by about a foot because I overestimated the wind. …I’ll have to start keeping score on this one, and attempting to make first-shot hits at long range more often instead of purposefully starting shorter and working my way out there!…

  9. Still can’t wrap my head around the north south still hitting right in the northern hemishere. Seems you would hit right shooting north and left shooting south

      • No. Read the car or merry-go-round examples. You hit RIGHT regardless of whether you’re shooting northerly or southerly if you’re in the Northern Hemisphere.

        Again, you’re either shooting North and you’re moving faster to the right (East) than your target so you miss to the right. Or you’re shooting South and your target is moving left (East) faster than you are so you miss to the right. See the speeding car and stationary target in the field example…

        • Yeah (hangs head low), I see it now. You are correct as usual. Thank you for being patient with your readers!

    • I think their analogy is flawed. The shooter and the target are moving in the same direction and speed so bullet time in barrel is mute.

      • They are not moving at the same speed. That’s the whole point. I used the analogy of a moving vehicle and a stationary target to make the velocity difference more extreme and easier to grasp. In real life, the velocity difference is extremely minor but it’s there. If you’re closer to the equator you’re moving East faster than if you’re farther from the equator. This is why you miss to the right whether you’re shooting North or South if you’re in the Northern Hemisphere. Read the car and target in the field example again for the description of how that happens.

        (BTW time in barrel has absolutely nothing to do with this and was not mentioned in the article whatsoever)

  10. I just read up on long range projectile ballistics. An interesting idea came to me. To have spin drift and Coriolis effect cancel each other out a bit wouldn’t it be better to have left hand spin barrel rifling in the northern hemisphere and right hand spin in the southern? Then you’d have less correction to make. Theoretically. I wonder if bench resters do that?

    • Additionally, another way to visualize spin drift effects would be a video of a soccer ball in flight or even a nerf football. There are vids showing the pressure difference on each side of the soccer ball struck off center that account for its spin and curvature in the air. These same vids show what happens when there is no spin imparted and you get erratic flight i.e., a knuckleball.

      • Yes, it would. There are some competitive shooters who do this for that purpose and some historical rifles, such as the Lee Enfield, were made with left-hand twist rifling for this purpose. We tend to spin bullets a lot faster than we used to, so spin drift is much larger than left/right Coriolis drift anyway, but there would be some amount of cancellation, yes. IMHO all long-range rifles designed for Northern Hemisphere markets should have left-hand twists. If nothing else, it would be great for their marketing haha.

  11. In utter seriousness, I offer the following mission to a well-heeled soul with plenty of money and time on his hands. Buy a fairly flat large plot of land, with one dimension of at least 1000 yards. Have a barn or build one at one end. Assemble a shooting bench on the other, facing the broad side of the barn at an angle of exactly 90 degrees and approximately 10 feet above grade. Make sure the broad side of the barn is at least 20 feet high. Paint a bull’s-eye at least 20 feet in diameter filling the broad side of the barn. Measure the exact distance from the bench to the barn and the azimuth(?) the shot will take.

    Fire away.

    Calculate.

    Publish results.

    Become even richer and more famous.

    • This is, in effect, what Brian Litz does, while also measuring speed and coordinates throughout flight.
      That’s why his balistic charts are different than other companies’ calculations.

  12. Fun fact: if you are a given distance south of the equator shooting at a target the same distance north of the equator (or vice versa), there is no Coriolis drift!

    • Yeah, that’s humorous, ( 😉 ) but it leads to a serious question –

      Jeremy (who spoke in class today) wrote :

      “• If you’re in the Northern Hemisphere shooting North or South, you’ll hit right of your target.
      • If you’re in the Southern Hemisphere shooting North or South, you’ll hit left of your target.”

      *Problem* with that – If I am on the physical equator firing north or south, is the Coriolis effect negated?

      If I am 1 km north or south, does the projectile somehow change trajectory as it crosses the equator traveling north or south?

      I may not be asking the question clearly, but do you see the problem with that explanation you gave?

      (I know, I know, I was a major pain-in-the-ass as a kid, and never grew out of it. It’s why I *snicker* quite a bit…)

      • @ uncommon_sense — that was actually mentioned in the article: “FYI, in the off chance you’re shooting across the Equator from one Hemisphere into the other at a target equidistant from the Equator as you, you’ll be spot-on.” 😉

        @ geoff — in my car example you are the equator and you fire out of either side. The effects mentioned are correct as long as the bullet remains either in the Northern or Southern Hemisphere and doesn’t cross the equator. If it crosses, it’s still the exact same thing that causes any drift: the difference between your speed and the target’s speed. You’re still both going East. If you’re both 10 degrees away from the equator, there will be no Coriolis effect. If you’re 20 degrees north and your target is 10 degrees south, your target is going East faster than you are and you’ll miss to the right. If you’re 10 degrees north and your target is 20 degrees south, you’re going East faster than your target and you’ll miss to the left.

        • Thank you for *trying* to explain it, I guess it’s above my pay grade.

          This subject makes my tiny head hurt…

          *sob*

  13. Anyone have better info/links/video on why shooting North/South deflects the bullet in the same direction? The physics in my head (and on a sheet of paper) say they should deflect opposite. The analogy in the article isn’t helping me.

    • I had the same problem. Then I started thinking about the factors involved.
      SPEED of rotation. If shooting north, your target is moving slower (smaller circumference) if shooting south, your target is moving faster (larger circumference ) based on northern hemisphere. The effect is based on SPEED of rotation of a sphere at different latitudes.

    • The bullet isn’t being deflected. The bullet is going straight. The Earth is moving out from underneath it. Randy explained it well (I tried to with the car example). Northern Hemisphere: If you’re shooting South then the target is moving faster than you are and you hit behind it, which is to the right. If you’re shooting North then you’re moving faster than the target and you miss in front of it, which is to the right.

    • You are right. On northern hemisphere your hit will go right whether you shoot north or south. Your right. And you turn 180 to shoot to opposite direction, so shooting north right means east and shooting south it means west.

  14. “Extreme Long Range Shooting Beginners”

    I don’t think shooting beginners at long range is really fair. If beginners are to be shot, they should be shot at close range so they have a chance to defend themselves, which would be consistent with “fair chase.”

      • Excellent article, more please. While familiar with the concept, I didn’t appreciate the amount of drift at reasonable ranges. The left hand twist in barrels for the northern hemisphere seems like it would be a given.

      • It was a good article. I had heard the term, but didn’t know what it was so I’ve been educated. When I was reading the article and trying to picture the explanation I got confused on the earth spinning to the west part, didn’t make sense so I looked it up and sure enough it spins to the east. I’m sure it was just an editing error, but wanted to point it out in case anyone else is as easily confused as I am.

  16. The effect on your bullet when shooting E or shooting to the W is not Coriolis, common misconception. It is actually referred to as the Eötvös effect. Coriolis is the effect of shooting N and S.

  17. As a knuckle dragging, Neanderthal, OFWG, bitter clinger, deplorable, MAGA type I thought the earth was flat. The only thing I know about the Don Cornelius effect is that gunnery sergeant Bob Lee Swaggart says you need to calculate for it in a one mile shot. I just figured I’d get closer to em and it wouldn’t be a problem.

  19. Unlike the cancelling-out effect of shooting a target equidistant across the Equator, it seems to me that if you shoot across a Pole to a target on the other side it will match the hemispheric error, even exaggerate it. That is, fire across the North Pole and you’ll miss the target right; fire across the South Pole and you’ll miss the target left. There would be no rise or fall of the target.

    And, while the Earth’s rotational motion is extremely small near both Poles, you and the target would be moving in opposite directions and therefore your relative motions would be additive. Shooting across a Pole would exaggerate this right/left error more than a shot taken simply near the Pole.

    • Yup. Instead of simply moving in the same direction as the target but a little faster or slower, you’d be moving in opposite directions. This aligns exactly with the merry-go-round example in the article. It’ll be a cold day in hell, though, before I’m shooting over either of the poles 😉

  20. ahh.. brings back memories… way back, I wrote a ballistics calculator program for a scifi author friend of mine.. he wanted to accurately depict artillery and long range shooting on the surface of a ring world..
    yes, I am a gun nerd.

  21. I saw flat earth thumbnail and thought “I’ve got to see the comment section.” Unfortunately I was a bit dissapointed.

  22. I can accept the East-West correction due to rotation but struggle a bit with any appreciable North-South deviation at even “long range” 1000 yards…here’s why:

    In a Nth-Sth firing direction orientation the projectile in the firearm and the target (and all other material things) are moving at approximately the same speed relative to the east-west earth rotation. The projectile has an initial e-w velocity due to earth’s rotation while it’s still cold in the breach, travelling down the barrel and this velocity isn’t lost by any force after it leaves the muzzle.

    I could understand the speed differential coming into effect at firing between significantly different latitudes over greater distances ( many miles) but for conventional rifle ranges don’t accept this is discernable.

    Brain teaser: the earth doesn’t rotate 360 degrees in 24 hours… go figure!

  23. Article is consistent with firing calculations for Honest John Rockets for ranges out to 20 miles or so. Initially designed for 500 lb warheads to be used in the Korean War. Converted to 20 kT nuclear warhead for Europe 1966. Not sure why to correct since, like horseshoes, close counts with this baby.
    For you artillery fire direction controllers: how do you correct range probable errors on a sloped target area?

  24. My 20 MOA scope base is wrecking my Strelok app results…I don’t know how to account for it…other than replace the mount to a zero MOA

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