Coriolis Effect half value?

[Danny Butler]

Dude, I think your reading into this way more, the OP said nothing about hunting, this is ballistics, if we are just trying to cold bore a piece of steel this is enough to put you of especially on a slower round at long range. My 6.5 that runs 400 fps faster than the Creed I have and will wack deer and elk at a grand with it, shot more than a few in the neck at 800+ so with that I see a 1/4 moa swing which is enough to miss the center of the vertebra hence I take any dialable effect into account, why not, does nothing but improve your solution!

I stand corrected sir...

 

[Snowbird]

as far as hunting goes, i restrict myself to shots i make 95-100% of the time. my fierce 7mm mag (3320fps) is comfortable to 600 or so. my 270 wsm was fine to 500. i might be able to stretch my 300wby out a bit further but have a long way to go before taking shots at game beyond 700. i generally enjoy the sneak but will take longer shots later in the season. but even then it's first round hits below MOA that count.

though i might think about taking the 6.5 out for some antelope due to how nice she shoots.

 

[bigngreen]

Part of that 100% shot percentage is the confidence in the quality of your solution, I practice in the mountains I hunt in so if my solution looks like a 2 moa scatter gun that just flat won't cut it, peeling off the different layers of a quality ballistic solution IMO let's you concentrate on the factors that really screw you like wind reading, rifle set up or animal behavior, I'm not into thinking about anything but the quality of the human element I bring into it. Same thing goes for long range hunting as for bow hunting for me, when I'm dialed and the cross hairs are settling or I'm at full draw in death mode.

 

[tony d willIiams]

Don't forget to correct for magnetic declination or your numbers will be wrong. Magnetic declination changes based on where you are on the planet. Coriolis adjustments of useful accuracy require that you account for the fact that true north and magnetic north are different but people tend to get their heading with a compass which is giving the user magnetic north.

There's no such thing as a half or quarter value for it (coriolis adjustment) unless you're academically multiplying by .5 or .25 because that's not how angular systems work. If you were to do it the old way shown in military field manuals then you'll be doing it wrong. Doing it wrong will have less of a useful effect than not doing it at all.

<rant> As a sort of side note: The military field manuals do the whole full/half/quarter value nonsense because it's close enough to put bullets at heads-down effect close and it's easier for people with 2 digit IQ's to understand than angle cosines, not because it's "correct". The technically correct way of adjusting for things like that is with angle cosine multipliers. </rant>)

Assuming a magnetic declination of 0deg for simplicity, a 45deg shot angle offset from true east or west produces a cosine of ~.7, not .5. So, if you were to have an indicated full value correction of .1mil for true west then the adjustment for north west (45deg north of true west) would be .07, not .05 as one might think. If you're anywhere near the Mississippi river then it doesn't matter much but as you get near the coasts it starts to matter a great deal as far as the whole thing goes.

Which brings me to my 2nd point: You're getting into the weeds by even bothering with vertical coriolis at such near distances. 3" at 1000yrds is very roughly .1mil which is smaller than the normal average group size from a highly skilled shooter with a highly tuned rifle and it's inside the vertical dispersion that a normal shot-to-shot velocity dispersion would generate. Meaning, you're trying to dial for something that's basically noise. Don't waste the effort. Bothering with it inside of a mile just makes the maths intensely and ridiculously more complicated than it needs to be.

I like your numbers and explanations. I will check with my data that I am growing. I enjoy programing and writing sequence just because it is a blast for me. Thank you for your explanation.
I am in process even though not needed just to do something being retired and all.

 

[dfanonymous]

The OPs question was seemed purely in ballistics. The hit percentage on anything however does have to do with the target size, gun capability and es and sd's. The further out you go and the smaller the target the less your hit probability is, and the more dialed in your OVERALL solution is going to need to be.

Add hunting into the mix, there's a slew of other questions. Been gone for a little bit and people are still talking about a 6.5's capability at long range killing. Or terminal performance. Fact is, outside of bullet perforce externally, the design of the bullet alone is important, something that no one ever agrees on, and of course your wind calls.

Wind I always put into a separate category because you're either good at it or not, as it pertains to taking a life. Not 50% correct when shooting steel, 70% of the time. At extreme ranges reading mirage is about the only way to get a accurate mid and far wind. Something probably not practiced on here much.

If you can dope all your drifts including Coriolis it's not a horrible thing. However yes, it's not terribly relative, unless your goal is hitting a 2 moa target at 2 miles. Then it is relative.

 

[Greyfox]

For about the last ten years or so I have focused solely on the goal of perfecting my equipment and skills for 1000 yard medium game hunting(deer/antelope). I have hunted with 6.5x284's with 140 VLD's just about exclusively over this period. The sophistication of the current ballistic calculators which, if used properly, will miraculously correct for spin drift, correolis, and aerodynamic jump, and hand you an accurate ballistic correction on a silver platter. Early on, using a RF and what today might be considered a rudimentary ballistic program(comfirmed at range), I simply corrected 1-2 clicks for spindrift between 750 and 1000 yards. For correolis, at 1000 yards, and the rare shot beyond, I only correct 1 click up/down if shooting within a 20 degree window of west or east. This method/formula still works for with little difference, if any, in results over time at these hunting ranges. The ongoing mastery of the wind call has, and will continue to be the determining factor of whether the shot is taken, or not.

 

[BallisticsGuy]

thanks for the replies. ballistics guy, that's quite a comprehensive post. thanks for taking the time. my goal has been to get consistent 1st round hits on steel at distance with wind and other variables accounted for. what i'm trying to avoid is cumulative errors like left to right wind with spin drift (barrel threaded right) or shooting west at long distance when it is cold out/ east when warm. i was just unsure at what azimuth people commonly disregarded the coriolis effect. i have a factory 6.5cm that shoots under 3" groups consistently at 900 yards but haven't been able to shoot East or West with it. my other semi custom rifles don't do that. they'll hold MOA out that far though.

so for my rifle it seems anything under 600 yards on an moa plate i will not correct for. after that i will likely correct with .1mil if shooting due E or W respectively if i have an aggravating factor.

i'm really trying to get better at recording and interpreting my data. DOPE books aren't my thing but i see the value after trying to chase down previously gathered info. wish i would have started one sooner.

For what you've got going on and for what you're doing there's only 4 things you need to be paying any attention to at all and here they are in order of magnitude: Drop, Target Motion, Wind, Air Density (read temperature because small changes in barometric pressure don't have near the effect people think it does but modest air temperature changes can have pretty dramatic effects at long range). Spin is usually going to be inside the wind reading error and in any event in years of competition shooting at long range I've never once accounted for it and I don't know anyone that does account for spin with anything smaller than .30cal at 1000yrds or closer under match conditions (yeah, a lot of qualifications on that one but it's true and for technical reasons I advocate people shooting 6.5mm and smaller diameter projectiles at 1000yrds or closer to simply ignore spin drift). Coriolis can safely be ignored, period. Nothing you're doing requires bothering with it and bothering with it will probably help you miss.