Do Not Mount Your Scope Level

[SSgt G Cody]

One more thing, for you guys shooting well beyond 1000 yds.: The Coriolis effect is greatest when shooting N or S, and least when shooting E or W. It is also important whether rifle twist is L or R, and whether you are in the Northern or Southern Hemisphere! So many details to keep track of! Welcome to the sniper's world!

 

[Black Hat]

Shooting to a point where gyroscopic drift will become a factor to consider, would be negligible considering the wind drift at those distances.

Wind drift is difficult to separate from gyroscopic drift, so it requires a very precise wind and conditions call to see the effects separately, not to mention platform and shooter.

You will likely be using a sighter or two to zero on target, and the errors/anomalies estimated atmospheric conditions will make gyro drift insignificant.

 

[Greyfox]

One more thing, for you guys shooting well beyond 1000 yds.: The Coriolis effect is greatest when shooting N or S, and least when shooting E or W. It is also important whether rifle twist is L or R, and whether you are in the Northern or Southern Hemisphere! So many details to keep track of! Welcome to the sniper's world!

The major Coriolis effect occurs shooting East/West. Influence lessens to NIL as shot direction moves North to South. My 6.5x284 is influenced about 6" in vertical from full West to full East shooting directions . This is a 1MIL correction(+/-) in either direction at 1000 yards.

 

[SSgt G Cody]

True! Mis-stated NS, EW Coriolis effect late last night. Sorry! Corrected now. There is also a minor effect of lateral trigger pull (R & L). Wind is still the biggest error factor at very long distances. Enjoy your shooting!

 

[Hugnot]

Coriolis effect? TOF? How much can your target, fixed to the surface of a spinning planet, move under a flying bullet in 1.38 seconds? TOF @ 1000, 6.5 147 gr. ELDM @ 2850 fps MV..

The latitude of the shot is important. At the equator the rotational speed of planet earth is about 1,000 mph. The rocket guys like to launch their big projectiles near the equator, taking advantage of higher angular momentum.

Taking a look at the Hornady 4DOF program, windage values at zero wind speed, shooting a 6.5 147gr HELDM bullet at 2,850 fps. The deflection at the North Pole would be .55 MOA for a shot in any direction, at 45 degrees (mid Oregon), the deflection would be .77 MOA at any direction, at the equator the deflection would be .86 MOA for a shot in any direction. .86 MOA (equator) - .55 MOA(north pole) = .31 MOA or 3.1 inches at 1,000. The elevation at 45 degrees latitude (like Oregon) shooting directly north up 24.48 MOA, shooting east 90 deg. up 24.29, west 270 deg. up 24.66. >> 24.66 - 24.29 = .37 MOA or 3.7 inches elevation difference at 1000, enough to miss X ring.

A mil rad at 100 > 36 inches per yard X 100 = 3600/1000 = 3.6 inches at 100 > 10 times more or 36 inches at 1000. Having 1/10 mrad elevation dial clicks this would be one click or 36 X .1 = 3.6 inches.

I like the tall target, like getting a group to hit at a plumb line making an elevation to hit at 1000, thinking that any existing wind affects would be more important than the Coriolis effect, provided the target was closer than several miles away. I like zippy bullets & most of my targets are less than 600 yards distant.

 

[Beluebow]

For those that don't have the time or inclination to dial spin drift out....I would hate to see what your mental wind picture looks like. A R-L wind is worth less value than a L-R when conditions appear to be the same.

 

[bigngreen]

If we are talking about long range shooting at steel or targets, carry on.

If we are talking hunting, I wonder if we have actually taken hunting to sniping?

I am beginning to wonder if we have evolved or devolved in the evolutionary food chain.

In our pursuit of one upping, I think we have jumped the proverbial shark.

Makes me wonder how archery hunters succeed with a stick and string.

You realize your posting on a Long Range Hunting forum right?!

 

[bigngreen]

This forums seems to have drifted back to the retarded SpinD days when the mantra was "why worry cause you can't shoot it".

Well it seems every gun on this forum is a .2 at largest gun you then can shoot it! One major gain in cold bore long range hunting was realizing that you can easily take into account what many think is lost in the noise, the more you take into account the less noise you have to loose stuff in and the wider wind margins you have.
It's amazing how much better wind calls you can make if that's all your doing, if every shot you know when it's outside the rifles capability it was one of only a couple factors which you can learn from and start bringing your cold bore in tighter extending your range and giving you far more room for error.
There is zero reason to accept minute of deer or elk, this forum is about precision hunting, if your bullet doesn't impact where your cross hair is holding you missed, figure out why and fix it!! Minute of deer or elk as acceptable is embarrassing!!!

 

[HockeyDad]

Does anybody worry about the CE?
.
.
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The Caffeine Effect?

 

[L.Sherm]

There is zero reason to accept minute of deer or elk, this forum is about precision hunting, if your bullet doesn't impact where your cross hair is holding you missed, figure out why and fix it!! Minute of deer or elk as acceptable is embarrassing!!!

Bigngreen 100% agree.

 

[JustMe2]

Sorry Greyfox, you have it backwards. Largest right/left CE occurs if you are shooting north or south. The circumference of the earth decreases as you move away from the equator causing the earth to rotate faster at the equator and slower as you approach the poles. This is the basis of CE as I explained earlier. North hemisphere the error will always be right and south hemisphere will be left. Also shooting East will cause an error high and west an error low because the earth's curvature falls away from the bullet shooting east and rises shooting west.

 

[Papa762]

In a previous thread, a forum member stated he intentionally sighted in his scope to hit the target to the left of the 100yd bullseye to compensate for spin drift and Coriolis at longer ranges.

Question: what are your views about using a tall target to mount your scope with an intentional calibrated cant and not level?

Procedure: Draw 2 lines on a tall target, one line being straight up/down level like is normally done, then draw a 2nd line in a "V" shape to the left originating at the 100 yd zero. As the 2nd line is drawn upward from the 100 yd zero, it should get further and further away from the level line. The result being at the 1500 yd point on the target the "V" line would be maybe 3-10" to the left of the center/level line.

Now place the rifle level in a vise and zeroed/sighted-in at the tall target placed at 100 yds. Next, loosen the scope and cant it, keeping the rifle level, to align the scope reticle with the "V" line and not the level line. This would put an intentional ballistically calculated cant in the scope to compensate for your rifle's spin drift and Coriolis as you dial the scope upwards. Now during a hunting situation, you'd only have to compensate for wind holds and not worry about adding spin drift or Coriolis.

So, what are your opinions of putting an intentional cant in your scope while mounting it?

That seems like really a fix for a non-existing problem at that range. You won't see Coriolis and spin until you do really long range, and then you'll have some other effects to worry about. This is the place to get the info, however!

 

[Greyfox]

Sorry Greyfox, you have it backwards. Largest right/left CE occurs if you are shooting north or south. The circumference of the earth decreases as you move away from the equator causing the earth to rotate faster at the equator and slower as you approach the poles. This is the basis of CE as I explained earlier. North hemisphere the error will always be right and south hemisphere will be left. Also shooting East will cause an error high and west an error low because the earth's curvature falls away from the bullet shooting east and rises shooting west.

Well, a bit of a play on words/interpretation. Yes, the larger effect of "left/right" is North and South. When speaking about the predominant effect of CE, as we experience, and correct for it at the longer ranges in North America is up/down when shooting East/West.

 

[Andrew Massi]

Anyone shooting long enough to warrant accounting for coriolis ought to have a balistic solver capable of accounting for it. Trying some nonsensical hack like .2 mil left zero @100 seems downright foolish to add a variable into the mix that can be easily effed up in the heat of the moment your adding math when it isn't needed.
The best zero for any long range work is, was and always will be poa/poi.