spin drift & Coriolis effect

[bigngreen]

Yes, it does depend on the direction you are shooting in conjuntion to true north/south. It will not always make your bullet drift right like spin drift from a right hand twist barrel. I believe the the poster below didn't quite catch onto your question.

It was my impression that Coriolis will have the same right component for any given direction but the vertical component changes with direction of fire.

I've found taking drift and Coriolis into account to be very beneficial for my wind calls now that I base it on what's actually going on not chasing "noise".

 

[rem]

I do agree with all of you that all of the little things add up. and i personal wont take a cold bore shot at an animal that I don't know I can make. If you can hit a 10 area at 1000 yards the first time you are the man! my point was based on a gun that shoots 1Moa counting for .25 moa seems silly but if you know what it is then by all means account for it. there are so many conflicting pieces of info on the subject I don't know were to start, except for shooting at all ranges and writing down the results. theory is one thing results are another.

 

[rscott5028]

It was my impression that Coriolis will have the same right component for any given direction but the vertical component changes with direction of fire.

I've found taking drift and Coriolis into account to be very beneficial for my wind calls now that I base it on what's actually going on not chasing "noise".

I believe you are correct.

In the northern hemisphere, the shift in POI due to coriolis will apparently be to the right regardless of whether you are shooting northbound or southbound. This seems counter-intuitive to me. But, here's my understanding...

When you face south, the gun and the bullet are travelling right to left which will "fling" the bullet to the left. However, the target to the south is closer to the equator and will travel from your right to left faster than the bullet is being "flung". Hence, you will end up hitting to the right of your POA.

Conversely when shooting north, the target will be moving from your left to right, but not as fast as the gun/bullet originating closer to the equator and thus being "flung" from left to right faster than the target is moving. As such, you will again hit to the right of your POA.

NOTE: The following 2 statements are incorrect as you'll see if you read subsequent posts...
Shooting westbound, the target will be closer on impact than it was when you squeezed the trigger. So, impact will be higher.

Conversely shooting eastbound, the target will be farther on impact than it was when you squeezed the trigger. So, impact will be lower.

Fortunately, we have computers and lots of gadgets to help us account for this. Whereas, I feel that spin drift may be somewhat more affected by the bullet and individual rifle. No doubt, everyone has an opinion about that.

-- richard

 

[RDM416]

....... I don't know were to start, except for shooting at all ranges and writing down the results. theory is one thing results are another.

rem,

That is a great place to "start" and to stick with. I have log books going back over 20 years with my shooting and loading info. Thing is, the longer I play this game the more detailed my log books get. I used to just write down load, weather conditions, and velocity of each round. Now in addition to that, I sketch out groups with each shot numbered (not always but often). I will often make notes of something that did not perform like it should have so I can remind myself and think about it later, etc..... Write down everything..... then refer back to that data, that is where you will learn the most, not when you are actually on the range.

I used to ignore spin drift and coriolis in my calculations and "dope". However, from real world experience I was quite well aware that the further out I shot the more my groups drifted to the right. At 1000 yards I would be about 1/2 to 3/4 moa right. I knew this and compensated for it even when shooting critters at those distances, so even though I did not understand WHY it was happening, my log book assured me it WAS happening so I compensated for it.

After reading Bryan Litz's book on ballistics it dawned on me that the advice I had been using of "spin drift and coriolis are too small to matter" was BAD advice, so now I calculate and compensate for both.

There is no substitute for range time, but make sure you are LEARNING something with your range time, otherwise you are just burning powder....

 

[tresmon]

Bravo4,

right yeah, cori is different for different coordinates and range.

Per my classes yeah it's looking to be well received and desired by many shooters. It's come to where I getting a website together so they're probably going to be a consistent thing.

This is a great topic! Thanks,
Tres

 

[Imho]

For those who want a relatively simple explanation of the Coriolis Effect, try THIS link.

Unfortunately, like most complex subjects, the explanation may raise more questions than it answers.

The net effect in terms of impact changes is actually a combination of multiple factors, even when facing directly North/South or East/West.

 

[BryanLitz]

Here's another resource for spin drift and coriolis effect:
spindrift
-Bryan

 

[rem]

For those who want a relatively simple explanation of the Coriolis Effect, try THIS link.

Unfortunately, like most complex subjects, the explanation may raise more questions than it answers.

The net effect in terms of impact changes is actually a combination of multiple factors, even when facing directly North/South or East/West.

thanks for the link.

 

[Imho]

Shooting westbound, the target will be closer on impact than it was when you squeezed the trigger. So, impact will be higher.

Conversely shooting eastbound, the target will be farther on impact than it was when you squeezed the trigger. So, impact will be lower.

Although your reasoning seems logical, the actual forces at work result in the opposite effect.

People quite commonly refer to the Coriolis Effect when talking about two separate effects, the actual Coriolis Effect and the Eötvös Effect.

At the risk of over simplifying things, the Coriolis Effect refers to the projectile (seemingly) deflecting horizontally and the Eötvös Effect refers to the projectile deflecting vertically.

In short, the Eötvös Effect results in Eastward moving objects having less gravitational force applied over their journey (in the case of a projectile the POI will therefore be high in relation to the POA), and Westward moving objects having more gravitational force applied (and therefore the POI will be low in relation to the POA).

I'm no expert, so I hope I've explained this correctly. The actual mechanics behind the "forces" at work really does my head in.

Just knowing that these factors exist is probably enough for most. Leave the mechanics to the physicists and actual values to ballistic software.

Fortunately, we have computers and lots of gadgets to help us account for this.

Exactly.

 

[rscott5028]

Yes. I had my wires crossed.

Bryan's website has a great explanation and he's the expert.
spindrift

 

[load]

So was this supposed to say you add 3" right for Spin Drift and another 3" right for Coriolis? If so, I hate to tell you this but you cannot just put a number on Coriolis like you can Spin Drift because it is never gonna be constant...unless you are shooting at the same range (and I don't mean range as in distance, I mean range as in Firing Range/shooting spot).



Yes, it does depend on the direction you are shooting in conjuntion to true north/south. It will not always make your bullet drift right like spin drift from a right hand twist barrel. I believe the the poster below didn't quite catch onto your question.

actually it does alway cause an impact right unless you are in the southern hemisphere in which it will ALLWAYS be LEFT. just as a left spin will cause left drift.
if you dont beleave me shoot out to 1760 yrds and do as you describe. you WILL be WAY off if you try to adjust for a impact left corialis in the northern hemisphere no matter the direction u shoot.

the adjustments i list will get u closer than u can dial anywere in the usa(except alaska), given mean velocity of 2800 fps (a good median for most types of rifles)and bc in the high 5's

 

[rem]

i was looking at the link to Applied ballistics the equation for the gravity multiplier accounts for muzzle velocity but not flight time how can it be accurate? if it is going to account for the velocity shouldn't it account for the average velocity. has anyone tried to use this equation with success? either it should account for the velocity and distance or just come up with a gravity multiplier for a direction and longitude. I put the equation into excel and got completely different results. Can someone who is smarter than me tell me what I am doing wrong?

http://www.appliedballisticsllc.com/index_files/vert.pdf

 

[Imho]

Once again, I'm no expert, but the way I read the formula it is producing a "multiplier" which his then applied to the (already calculated) effects of gravity in the bullet drop mentioned in the example.

 

[Imho]

In Excel the formula for the cell would be:

=1+2*0.00007292*2870/-32.2*COS(RADIANS(45))*SIN(RADIANS(270))