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Old September 19, 2012, 08:20 AM   #26
tobnpr
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^^^
This.
With an 8 twist and 80 grain bullets it would do the job...

But if you have a 14 twist and are limited to the 50 grain bullet with a lousy BC it's going to be an uphill battle.

Reasonable?
That's in the eye of the shooter. There are guys that like to shoot VLD .223's to 1000 yards. Not my cup of tea, though...
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Old September 19, 2012, 07:22 PM   #27
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If one checks the ballistics of bullets fired from .308 win. cases in 24 to 26 inch barrels, they'll see the following trajectory data for a 1000 yard zero:

Bullet drop at 1000 yards ranges from about 420 to around 480 inches; your sight will need 42 to 48 MOA elevation from boresight to zero at 1000 yards. Most bases and rings for a given receiver are set to put the scope's mechanical axis parallel to the receiver axis. The bore axis may well be off by several MOA. So your scope needs to have at least 50 MOA elevation up from optical zero in the scope if you want to use the same setup for ranges from 100 to 1000 yards. Or, use a 20 to 30 MOA angled base. Don't shim a rear base; that'll put the ring axis on it above the front ring and sometimes bends scope tubes when they're clamped in hard. One other thing, optical zero in the scope's probably not half way between the E and W adjustment limits. You can find the scope's optical zero by spinning it in two V blocks then adjusting E and W until the reticule stays on the same point as the scope goes round and round.

Highest point in the trajectory is about 12 to 13 feet at around 600 yards. Winds up to 12 feet above ground are fairly even in speed. The wind closest to the firing point has the greatest effect at the target. So pay close attention to the wind for the first 300 yards where the bullet's under 10 feet above the line of sight.

Last edited by Bart B.; September 19, 2012 at 09:15 PM.
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Old September 19, 2012, 09:36 PM   #28
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Quote:
Highest point in the trajectory is about 12 to 13 feet at around 600 yards. Winds up to 12 feet above ground are fairly even in speed. The wind closest to the firing point has the greatest effect at the target. So pay close attention to the wind for the first 300 yards where the bullet's under 10 feet above the line of sight.
I disagree with that. The wind has the most effect on the bullet at half to two thirds distance the target. That is where the bullet is at it's highest arc and where its most directly into a "full value" wind effect.

Take your range flag, hang it at 30 ft, or at the top of the pole. Take a second flag and hang it on the pole at barrel level. You'll see the wind is completely different at 30 ft and ground or barrel level. The bullet would be more effected at its highest arc more then at the barrel or shooting level.

This chart explains it a bit better. We know a partial value of wind has less effect then a full value. The chart shows what part of the bullet's flight that is in the "full value" of its path.

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Old September 19, 2012, 11:18 PM   #29
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Sierra Bullets Ballistic Software used to calculate the following for a .300 Win. Mag. cartridge:



Drift at 900 yards for wind only in the last 300-yard segment's about 1/3rd of what wind only in the first 300-yard segment.

For wind only in the middle 300-yard segment, drift at 900 yards is a little more than twice what wind only in the last 300-yard segment has at 900 yards.

The bullet's drift rate increases with range but the distance to the target gets less with each range band further down range.

Reading the mirage through a spotting scope will reveal the wind at the top of the bullet's trajectory moves at the same speed as it does in the line of sight. The wrinkles high and low all have the same speed; they move together. If the wrinkles at the high point of the trajectory did move faster than the lower ones, it would be easily seen.

Normal come up on M1 and M14 sights going from 600 to 1000 yards is about 23 clicks/MOA for .308 Win. ammo. At 600 yards, that moves the bullet trajectory up about 12 feet at 600 yards; the average high point in its trajectory to 1000 yards. The wind atop a 30 foot pole is over 15 feet higher than the bullet's path; it doesn't effect the bullet at all.

Last edited by Bart B.; September 20, 2012 at 12:47 AM.
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Old September 20, 2012, 07:45 AM   #30
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I have no knowledge of whether the wind is more consistent near ground level, or higher as is being discussed.

But seems that discussion is relevant to the "wide open spaces", and not high-berm, enclosed shooting like the 1000 yard range we frequent.

The high berms cause confusing, swirling winds...like being down in a punchbowl.

The last 400 yards (beyond the 600 yard berm) is called the "ditch"- because it's literally that- a 400 yard narrow ditch surrounded by high berms.

Completely different wind effects...a real challenge

http://manateegunclub.com/index_files/SateliteView.htm
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Old September 20, 2012, 08:26 AM   #31
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David Tubb is probably one of the best long range shooters this country has ever produced.

He is the one that demonstrates using the range flags to show where the wind is most effective. He simply does what I mentioned earlier. A flag pole is about 30 feet tall. He puts a flag at the top of the pole and one at the bottom, the wind speed is normally different, and may be even blowing a different direction.

Even on flat ranges there is going to be something on the ground to disturb the wind.

Just ask yourself why the Army Marksmanship Unit, and everyone else experienced in long range shooting tell you to focus your scope at Midrange to 2/3 range, to read mirage and other wind indicators.

To see what wind really does, you can put the numbers in a BC program OR you can go to the range with a good spotting scope and see for your self.

Get right behind the shooter and observe the trace of the bullet, on a full value wind coming from 3 o'clock, you see the bullet start our toward the right and when it gets past mid range starts a sharp turn back toward the target, much like the picture I posted above.

At 1000 yards, (which is what the OP asked about) the 308 arc is between 30-35 ft above the ground.

That is the wind you should concern yourself with the most.

As to hand held wind meters. They are great, but not for what people think.

People take a reading on the firing line, and that's what they use to adjust their sights. But that isn't the wind they should be reading. They should be reading the wind at the height of the arc.

Thats where mirage comes in if there is no range flags.

To learn mirage is where the wind meter comes in. Go to the range or open field, leave your rifle home, and take your spotting scope and wind meter.

Get a reading (doesn't matter where) then look through the scope and see what the mirage is doing. What you are trying to do is learn what the mirage does at different wind speeds. You can do this at different angles to get the ideal of the mirage at different values. It doesn't matter how high off the ground, air movement is what you're looking at so you can get an idea of what mirage looks like at different wind speeds.

You do this a bit, then when shooting, you can focus your scope at 1/2 - 2/3 distance to the target at the max arc of what bullet you are shooting and get the best reading of the wind (mirage) to get you on target.

Here's a hint about focusing the scope and reading mirage, Be careful you don't go the wrong way. Meaning be careful you don't focus the scope past the target. Doing so will reverse the mirage.

I found this out the hard way when I attended the NG-MTU Coaches Clinic.

We were on 600 and the ALL Guard Shooters were taking our call. In other words they were making the corrections we were giving them, right or wrong.

After the targets were run up, showing the hits, I was on the opposite side of everyone else. Because I was focused beyond the target the mirage was reversed.

I don't have to tell you how embarrassed I was when shooting was stopped and the whole line of future coaches was brought to my point to be shown WHAT NOT TO DO.
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Old September 20, 2012, 09:03 AM   #32
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Kraig says:
Quote:
At 1000 yards, (which is what the OP asked about) the 308 arc is between 30-35 ft above the ground.
Fine. How do you suggest all the ballistic software out there get changed to do that? Berger's and Sierra Bullet's software is probably the best available. They put the maximum ordinate for .308's zeroed at 1000 around 12 feet near 600 yards.

If what you say's reality, then please explain why coming up 23 to 24 MOA from a 600 yard zero to a 1000 yard zero puts bullets from a .308 thirty feet or more above the 600 yard target when 23.5 MOA at 600 yards equals 11.75 feet. Download Berger's software and see for yourself.

I already know all that other stuff you mentioned. And more than a few of us High Masters in NRA long range matches have confronted David Tubb about his areas of ignorance.
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Old September 20, 2012, 09:14 AM   #33
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Maybe we aren't on the same sheet of music.

I do use Berger's program, and if you use a 1000 yard zero (which you would be using if you're shooting 1000) the highest arc of the bullet will be about 600 yards, and that is where you should be reading the wind when shooting 1000 yards.

The flag pole was used as an example to show you get a more accurate wind reading up in the air then you would at ground level.

Just forget the numbers, set your BC program with a zero at the range you're shooting. It will then give you the max arc, which will be about or just beyond mid range.

And that's why the AMU, and Tubbs recommend reading the wind/mirage at mid to two thirds distance down range.

I think we are bantering semitics.
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Old September 20, 2012, 09:56 AM   #34
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Kraig, here's what I set Berger's software to:

Standard defaults used except as follows.....

Zero and max range at 1000 yards, range increment at 10 yards.

Bullet at .308 diameter, 175 grains, G1 BC at .490 (for Sierra's 175 HPMK), muzzle velocity at 2650

Highest bullet's trajectory above line of sight happened at 570 yards with 142.96 inches above line of sight. That's 11.91 feet.

Use these inputs with your Berger software and we'll compare notes. Maybe those "notes" will be good for the "music" we're discussing while bantering semantics.

You can also use Berger's software to see why wind closest to the firing line has the greatest effect on drift at the target. If you trust Berger's software to be accurate.

Last edited by Bart B.; September 20, 2012 at 11:12 AM.
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Old September 20, 2012, 11:11 AM   #35
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I used the 175 @ 2550 (my M1A or 308 target rifle I use) and the altitude for my area (4500 Ft). Which gets us pretty close to the maximum ordinate of the 308 shooting at 1000 yards which is just beyond mid range.

Which I believe is the point at which wind has the most effect.

Of course different bullets and different velocities means a different max ordinate but they are pretty much between mid and 2/3s range to the target.

We talk about wind effects but the most critical is in overhead fire. (Where you are covering advancing troops)

To figure the abscissa (distance from the gun to the ordinate we need to know the ordinate in mils, its value in yard to determine the max ordinate.

The Formula is W=R*M/1000

Where is R = the abscissa
M = the difference of angle of departure in mils between the abscissa and the target

W is the max ordinate.

I had to teach this when running machine gun schools teaching overhead fire to determine the safe areas between the gun and the target.

Lets say we are using the 150 grn 30 cal bullet at 2700 fps (typical machine gun ammo.

The angle of departure for 1000 yards would be 14.047 mils
The angle of departure for 600 yards would be 6.009 mils.

14.047-6.009 = 8.018 mils

600 * 8.018/1000 = 4.810 yards or 14.43 feet

do the numbers for the for 700 and 800 yards (angle of departure is 7.598 and 9.443 respectively) you'll find in this case the max ordinate between the rifle and target is at 700 yards or about 16 feet,

7/10s is still pretty close to 2/3s distance.

If you don't have a method of determining angle of departure in mils remember 17.7 mils in degree or 3.437 minutes in a mil.

Yap you can get the same thing from a BC program, but we didn't have such programs (or computers) when I was in the game.

The point being the above math will check your BC program AND confirm the max ordinate will be between 1/2 and 2/3s distance between you and the target. And that is where you get the most effect of the wind.

I know a lot of this seems off topic but in reality it isn't.

We had this problem come up on our clubs range. The power company put some power lines across our range. We had to set our 300 yard targets where the max ord. of pretty much any round wouldn't hit the power lines.

Using the math posted above, shows that since the power line is less then half way between the firing line and the 300 yard line, we could shoot rounds with a max ordinate that exceeded the height of the power lines. Rifles werent the problem but pistols and BPCRs were.

Back to wind, get your values from 1/2 to 2/3s distance between you and the taget for the most accurate reading.
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Old September 20, 2012, 11:27 AM   #36
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Kraig, I used the 175 grain bullet leaving at 2600 fps (2550's the number at 26 yards where arsenals have their chronograph) at 4500 feet and got the maximum ordinate at 129.12 inches 560 yards down range for a 1000 yard zero. That's 10.76 feet.
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Old September 20, 2012, 11:33 AM   #37
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I swear you guys just blow me away with the depth of knowledge and willingness to share.

I am impressed.
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Old September 20, 2012, 11:34 AM   #38
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I think you're missing my point, regardless of heigth of the max. ord, it's still gonna be 1/2 -2/3s distance to the target. Whether its 2550 fps or 2650 fps. Whether its a pistol shoot 50 yards or a 260 Rem shooting 1000 yards.

Matters not whether you are using a BC program or math, the end result is the same as to where the max ord (what ever it is) will be pretty much the same 1/2 to 2/3s.

The Max Ord will be different of course, but the point of the max ord will be 1/2 to 2/3s distance to the target.
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Old September 20, 2012, 11:55 AM   #39
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Quote:
I swear you guys just blow me away with the depth of knowledge
Most of which is useless, I feel one would be better off taking his gun and and shooting it to see what happens.
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Old September 20, 2012, 12:49 PM   #40
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Kraig,

Don't know that I agree about "useless."

The science behind what makes things happen is fascinating to me.

There are facts you use and those that are tucked away. I do agree more shooting is a real benefit. It is also nice to know why things occur the way they do.

I really do find your posts worth reading.
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Old September 20, 2012, 12:51 PM   #41
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Thank you for that, Remember when I get onto a "Indirect fire with a rifle rant".
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Old September 20, 2012, 01:13 PM   #42
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Kraig, I'm not missing your point; I agree and have shown the max ordinate's 1/2 or a bit further than mid range. 560 to 570 yards in this situation.

My contention is how high above the line of sight it is. 11 to 12 feet above the line of sight for the .308's heavier match bullets is typical for 1000 yard targets. That's nowhere near the 30 feet you've claimed.

Now I gotta say I think you're missing my point.

The .30-06's 150 grain bullet (BC=.346) from machine guns leaving at 2700 fps has a maximum ordinate of 203.30 inches at 590 yards zeroed for 1000. That's just under 17 feet; the highest Berger's software says it goes above the line of sight.

Last edited by Bart B.; September 20, 2012 at 01:23 PM.
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Old September 20, 2012, 02:05 PM   #43
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The point I'm making is IT DOESN'T MATTER, how high off the ground the max ordinate is, whether its 1 ft, 10, feet or 100 feet.

What does matter is regardless of what you shoot, or how far you shoot the maxi mun ordinate will be between 1/2 and 2/3s distance from the muzzle to the target.

To determine wind correction, one needs to focus on the wind between 1/2 and 2/3s from your position to the target. That is where the bullet will be most venerable to the effects of wind.

Again, it doesn't matter what bullet, what velocity, or what range.

Take my 150 Gr LSWC with the BC of .286 at 1380 fps sighted in at 50 years. The max ordinate of that bullet will be at about 40 yards, or a tad above the 2/3s distance, but still to the point of max wind effect. (not that the wind at 50 yards is gonna throw such a bullet off enough to notice, but the principle is the same).

It would be hard to dispute the fact that the Army Marksmanship Unit has the best shooters in the world. Its their job, in cahoots with the CMP, to teach the military and civilians how to shoot.

To quote from the AMU Service Rifle Guide:

Quote:
The shooter is concerned with the wind between the shooter and the target, so focus the spoting scope short of the target...Typically, the focus will be about half way between the firing line and the target. Care must be taken not to focus beyond hte target, as this will sometimes produce a "reverse reading" of the mirage.
We can argue all day about whether the max ordinate is 10 feet, 20 feet, or 1/4 MOA (as in the 357 case above), it wont change the fact that the bullet will be most effected by wind at a point 1/2 to 2/3s distance to the target. whether that distance is 40 yards in case of the pistol or 700 yardes in the case of the rifle.

And that, what I thought was the orginal point of the discussion, "at what point does one need to read the wind to make adjustments to allow him to hit the target."
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Old September 20, 2012, 10:12 PM   #44
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I'll see what I can find to calculate wind speeds at different heights above ground.

Last edited by Bart B.; September 21, 2012 at 07:58 AM.
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Old September 21, 2012, 06:20 PM   #45
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I think under various circumstances you both could be right.
1) IF IF IF wind was exactally constant over the bullet's entire path. In this senario, the above picture of the prone rifleman's bullet drift would be correct. Meaning that a 10 mph crosswind would immediatly effect the bullet's path, and therefore, any immediate deflection counts much greater than deflection later. This scenario migh happen if you were in a tower, shooting across or slightly down towards a target. The wind could even be greater at the muzzle than anything else the bullet sees in it's path, if you were shooting down.

2) normal conditions - where the wind is 5-6 mph at ground level, 15 mph at 15' up. Here, the wind-influence drift would likely be greatest at the 1/2-2/3 distance, because the force of the wind at that higher point in the bullet's path is much stronger. However, if that same force had been acting on the bullet at ground level, you'd be back to scenario 1.

You guys are both right, but in most practical on the ground scenarios, concentrating on the wind at 1/2 - 2/3 of the way to the target will likely get you the best result. Wind velocity is usually variable, increasing with height from the ground. the picture of the marksman above does not take that into account.
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Old September 22, 2012, 08:19 AM   #46
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Yea.... it'll do that.

http://www.youtube.com/watch?v=xesBYKRzqew

30-35 minutes of come up required (around 10MIL if you're using a MIL/MIL scope).
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Old September 26, 2012, 04:31 PM   #47
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Seems there is a small reduction in wind speed from some height above the line of sight down to it. So Kraig's somewhat right. But it's not very much. Over short grass or fallow ground (wide open rifle ranges), at 15 feet above ground it's 15 mph. It'l be about 14.5 mph wind at 11 feet above ground (max ordinate for .308 Win. zeroed at 1000 yards), it will have an 11.5 mph wind at 1 foot above ground where the line of sight is.

But if the wind is constant at all heights, it's easy to figure with ballistic software that the wind closest to the firing point has the greatest effect. One needs to do this to proove my drift numbers in post 29 aren't what one thinks they should be.

Now I wonder what the bullet and ballistic software company's response will be when I email them my complete findings for wind shear numbers over several types of ground.

Last edited by Bart B.; September 26, 2012 at 10:11 PM.
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Old September 26, 2012, 05:45 PM   #48
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The problem is, the wind doesn't just effect the bullet along the line of sight.

Line of sight being X, the path of the bullet would be X+.

Lets use an angle firing example to show what I mean.

Lets say you range your target and find its 900 yards away at 15 degrees down (or up).

We know that you multiply 900 by the cosine of 15 degrees or .9659.

So 900 X .9659 = 869.31 yards.

So one adjust his elevation for 869.31 yards. HOWEVER, the bullet is exposed to the bullet the full 900 yards.

So you adjust the elevation for 869.31 and account for the wind for 900 yards.

It's better to use time of flight as to stright line distance as the bullet is effected by the amount of time its expose to the wind as opposed to the distance it travels.

If bullet A takes 2 seconds to get to point X, it be effected twice as much as the same bullet taking 1 second to get to the target.

I not a computer programer, but I'd assume your BC programs take into account the ARC of the bullet to compute TOF rather then line of sight.
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Old September 27, 2012, 06:45 AM   #49
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Wind in each column's based on a 15 mph speed 15 feet above the horizontal line of sight. As height decreases, so does wind speed as shown in the table. How much wind speed slows down depends on the terrain.

On typical rifle ranges (short grass, fallow ground) there's not much wind speed difference between the line of sight and maximum ordinate (bullet height above LOS) for 600-yard zeros with either the .308 or .300. More difference happens with a 1000 yard zero.

Last edited by Bart B.; September 27, 2012 at 09:29 AM.
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