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Monday, 12 December 2016

Long Range Shooting - A Load of Old Spin - Coriolis Effect & Magnus Effect:

Years ago back in 1835 - when they did a lot of history - a bloke called Coriolis invented a 'fictitious force' called the 'Coriolis Effect'.  - Before that - things didn't spin so much and just sort-of jumped up'n'down and wobbled a bit when they had earthquakes and stuff..

Long range shooters need to consider the Coriolis effect when shooting beyond a couple of hundred yards (it's even worse if you're using metrics eh).

The Coriolis effect is caused by the inertia of the Earth spinning to the EAST at around a 1,040 mph at the equator and this is easily observed now that we have man-made satellites - by the tendency of low pressure storms to rotate in a clockwise manner in the Northern hemisphere when seen from above.(That bloke Coriolis must have had a hunch eh)
Northern Hemisphere Storm.

 - and in the other direction in the Southern Hemisphere ..
Southern Hemisphere Storm.

From a shooting perspective in the Northern Hemisphere this will cause your shots to deflect to the RIGHT.

- While down here in "The Antipodes" our shots are deflected to the LEFT. (- Incidentally our antipodes is Spain).

When you are shooting roughly East-West (or West-East) in either hemisphere there is no sight correction required  - however if you are shooting on a North-South alignment you may observe this bullet drift - if the projectiles base is visible in your optics.

- Now feel free to argue about this among yourselves - but another example of the rotational effect of planet Earth is that your bath water will rotate anti-clockwise when draining in the planets'  upper half - and down here in the lower Pacific - it will spin clockwise.
'Pommie Plughole'

Confession: Now I have absolutely no experience of this because I have not had a bath in forty years (since coming to NZ). (- Mind you I have been swimming - does that count?)

Please do not confuse this Coriolis Effect with the Magnus Effect (invented by a different old bloke)- which is the "curve-ball phenomenon" resulting from the air moving differently on opposite sides of a spinning object. This causes a speeding bullet to 'crab' to either side depending on the direction of the barrel rifling. You need to consider 'yaw' together with the bullets centre of pressure - as opposed to its centre of gravity.

- Is everybody happy?

- This is slightly interesting too.. (Google is your friend)
E SHIP 1 Uses 'Magnus Effect' With 'Flettner Rotors'.
- Clever Germans eh!

P.S. I'm sure that those who have read this far will not be surprised to hear that the duration of a modern day is around 1.7 milliseconds longer than it was a hundred years ago - as the rate of Earths spin slows. This doesn't have much effect on long range accuracy but..

However - today's starter question for ten points: Which direction would you need to fly (in a long-range aircraft) to go directly to your antipodes?