9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

[Broz]

If anyone has a program to dope spin drift, I'd be curious to know what it is at 2000 yards!

At 2000 yards with my 338 LM and a Berger OTM 300 gr. with an altitude of 4100 and a MV of 2800 spin drift is 1.7 MOA. according to my shooter program which puts me pretty much on even at these distances.

With my 300 win and a 210 Berger @ 2995 fps. (which I have not shot this far) shooter says 1.9 MOA

Jeff

 

[Topshot]

I'm only interested in curing part of the problem in the 9 vs 3 oclock wind difference. By simply canting my scope a small amount and testing it to be about 3/4 moa , I no longer need to have a 3moa hold for one 2 mph wind and a 1 moa hold for wind in the opposite direction. Do it your own way, I have no problem with that. And Top gun, the spin drift does increase faster than the linear equations would suggest but the drop of the bullet is related to the velocity of gravity and since at 2000 yards , I'm at 93 moa, the canted allowance would be about 3.7 X the 1 moa for 1000 yards . a little over 74". If anyone has a program to dope spin drift, I'd be curious to know what it is at 2000 yards!

Paphil,
To work it out I would need to know the length of your bullet, the twist rate of your barrel, bullet weight, B.C. and your velocity to give you a figure.
Spin drift is a function of the above as well as time of flight and departure angle.
There are a few ways that spin drift is calculated on hand held phones and PDA's. One way is as a fraction of the standard US mil ball tables, another is by approximation calculations that simplify a lot of more complex models (As per "Shooter)". A third way is how Exbal does it by user input data from test shots but this gives a linear result as I understand it.
Its handy to know which way your program works for ELR shooting but not real important for out to 1K.
It can be measured with doplar radar.

 

[paphil]

Like I said earlier , what I'm doing is to help with the doping the wind. What is pretty generic at 1000 is not generic at 2000. When each degree temp change is 3 inches of verticle and 100 feet elevation is worth 6 inches of verticle, you better have a program to help! I'm not a scientist ,just want to help people shoot. I'm mainly concerned with hunting out to1000 and teaching the basics of what people need to know to make good shots. When you add angles to the shot, it gets even more complicated. I doubt the Canadian had any advanced math ability to shoot 2600 yards but he did it anyway! Be aware of the variables and you can correct for them. I do admire those of you who have the ability to calculate what you need to do to make long shots. But that said, I remember a similar post where a "scientist claimed that the only place to truely test spin drift would be in a vacuum! Da.... Without air there would be no spin drift! I don't know for sure but I would suppose there would be less drift at 10,000 feet than at sea level. Thinking is a good thing and if I get you thinking, someone will invent a better way than what I'm doing.

 

[Bart B]

To work it out I would need to know the length of your bullet, the twist rate of your barrel, bullet weight, B.C. and your velocity to give you a figure.

Because all rifle bullet's BC's change with their speed through the air, don't you need different BC's for different speed/velocity bands?

I would think so, but I might be wrong.

 

[ken snyder]

I'm leaving CE alone until I know which side my bread is buttered on. S.D. and a canted scope work very well when set up at the longest expected yardage. When closer ranges are shot the poi traverses closer to the center of the optical radius center and then past center keeps going (traversing), The closer the distance the less the error and the more poi can be off to hit the same size target. If a person sets up at a closer range and then shoots long range the error gets larger with distance and the target gets smaller ( not really). Setting up at max range reduces error from S.D. Setting up at close ranges increases error. I have no Idea what a rifle set up for ranges that span from 100 yds. to 2000 yds would be, Its got to be a bunch though. The only thing that makes the craziness of ELR shooting possible for me is to "use a dedicated rifle" and if I were to try to shoot closer ranges with them it would be a monkey and football show. Even at that I have very firmly hit a brick wall at 1800 yds and most folks will get frustrated to the point it seems like a joke to them and quit playing, It is quite the adventure!

 

[Broz]

Guys this might not be of interest but I will toss it out there for what its worth since it was just yesteday and fresh on my mind.

In talking with a few other wolf hunters I ran into while hunting an area, we got to talking long range. They wanted to see a LR shot and I am always eager to send one. So a rock was located at 1554 yards. Rock size was basically 2moa x 2moa measured with my NXS RN-R2 reticle. With all eyes and glss on the rock I doped the scope and sent one. Wind was very very light and I didn't even add it to the dope as it was so light and the target was so large. I hit about 1/2 moa right and 1/2 moa low from point of aim. I sent another using a little hold to center and we didn't spot it, I think it hit center rock but cant be sure. So I went back to the center mass hold like in the first shot and sent another. It landed in the same 1/2 moa low and 1/2 right spot as the first.

Now my point here is this. As I recorded this info in my field log book I wondered why I was 1/2 x 1/2 moa off. I had not employed the CE function as I felt I was good to go with out it. So I re-ran the dope on "shooter" this time elmloyng CE and getting the azmuth. The CE effect for this shot was another .4 moa left. Plus I believe I didnt give my kestrel time to get a good temp reading and that could easily have been the 1/2 moa low. My kestrel is pretty slow at temp readings I need to find a better way for getting current temps faster.

Anyway you cut it Corriolis Effect would have put me closer on this shot.

End result is, they were impressed and are coming to some of the long range shoots I do this summer. So I may have gave them the bug.

Jeff

 

[paphil]

That is what I was saying about temperature and altitude changes! At 1500 yards, 1 degree is about 1 inch vertical so if you were off by 7 degrees that could explain some of it. Also , a 1/2 moa gun could miss by that much. At that range even hitting the rock is a great shot!

 

[Broz]

That is what I was saying about temperature and altitude changes! At 1500 yards, 1 degree is about 1 inch vertical so if you were off by 7 degrees that could explain some of it. Also , a 1/2 moa gun could miss by that much. At that range even hitting the rock is a great shot!

Thank you, I do feel that the combination of this rifle, my ammo and I are a 1/2 moa combinaton at this distance. What I am saying is it will produce more 1/2moa groups at this range than not and most will be centeresd on point of aim as I have put a ton of time into fine tuning my drops in the program. That said, the shooting position was a bit uncomfortable for me so I could have been off a little, but what ever it was was consistantly off so I feel it was lack of the use of CE and bad inputted temp data on my part.

Jeff

 

[SBruce]

Hitting within 1/2 minute of your POA at 1550 yds first shot is pretty **** impressive Broz. Good Shootin!
I take it you were accounting for spin drift though somehow? Does your program calculate SD, or does it rely on a manual input like my NF Exbal does?

You're definately in the Elite class IMO. Right now, I'd feel really good if I could put the first round within 1/2 minute at 1000.

 

[ken snyder]

Broz It sounds like you did very well for our sport. I don't actually know if CE would have made a difference. Here is my counter point (just in general): It is our Scope adjustment ratio. Example: If a person uses a scope with 1/4 moa adjustment there is only a certainty of a little under 2 inches of accuracy from the scope adjustment at a little over 1500 yds. and that is up, down and left right. that in itself is 1/2 moa in total or about an 8 inch circle.

If you click stop on your scope had settled to the other side of true zero how much would that be off if it were in the correct direction. How much is a click on your scope ( I don't have one of the same brand) It is an interesting counterpoint and yes I am still confused by CE

 

[Broz]

SBruce, yes, spin drift was on. In the Shooter program you have the option to manually turn on SD and CD for each shooting solution or you can choose to have them included in every solution. I have the SD box checked to be included in each shot and is in every solution even when wind corrections are added. For the CE I usually anually turn it on by simply checking the CE box and then hit the "get azmuth" box. An asmuth function is part of the shooter program too, you point the phone and hit the hold button. You do need to know your current latitude tho. I gennerally use CE for any shot 1200 and farther but I was being lazy I guess.

Ken, Great point. My scope is a Nightforce NXS with .25 moa truuets. You are correct about zero's and clicks value. But the 8" circle is in the very worst senerio. I tend to zero to favor the left at a 200 yard zero when a click right moves me right of point of aim. The reason is, I usually error left on shots for what ever reason

There will always be errors present. What ever they were I still would have dialed that .4 moa left for the CE to the closest .25 moa which is .5 moa and the first bullet would have been center mass for windage. If I had turned on the CE option in Shooter.

If any of you guys are using Droid or the I phones I would really recommend the "Shooter" program. It is HIGHLY tunable to your rifle and scope values and is a HUGE value for $10

Jeff

 

[Topshot]

Broz, Excellent shooting. You sure have that rifle sorted out.



Hey just for fun guys, I have a trick question for you.

When would a bullet fired from a right hand twist barrel not drift to the Right?

 

[Broz]

Broz, Excellent shooting. You sure have that rifle sorted out.



Hey just for fun guys, I have a trick question for you.

When would a bullet fired from a right hand twist barrel not drift to the Right?

When you have a right to left wind or you are a long ways from home

Jeff

 

[ken snyder]

OK I'm convinced enough to start playing with and learning CE. However my cell phone wont make me happy for now ( I find them clunky to use ) I would like to know if there is an affordable program for my lap top or is the cost why so many are going cell phone.

I would like a good bullet library that is tweekable for B.C. that the program will correct for all the normal stuff with the addition of SD and CE without having to add in speculation or another set of numbers and latitude correcting for CE as well

Basically just enter the facts and push the button (lap top, because I use the armor plated phones that are just a phone, heck I even manage to destroy them once in a while

Which program do I want and who do I get it from!