How does as strong tailwind effect BC. If you are shooting a Juggernaut at 2750 and a 215 hybrid at 2550 and you get a extra 10mph gust, will the faster bullet with less BC impact the target higher than the slower bullet with better BC.
Tailwind and BC
- Thread starter jsthntn247
- Start date
XTR
F-TR obssessed shooting junkie
I don't know if the effects, or difference will be noticeable for most of us between modern bullet designs and speeds. I'm sure there is a calculator that will answer it.
With BPCR bullets and speeds (sub sonic most of the way to 1000) at 1000 yards the difference is quite large. Something on the order of a quarter MOA of elevation per MPH of tailwind. Keep in mind I'm talking about a bullet that takes 175 to 200 MOA to get from a 100 yard zero to 1000.
Then there are terrain effects. Some place like Oak Ridge, a headwind which ballistically should cause you to hit low, will cause you to hit 3/4 to a minute high due to the lift off of the berms/hill at 800 and 900.
With BPCR bullets and speeds (sub sonic most of the way to 1000) at 1000 yards the difference is quite large. Something on the order of a quarter MOA of elevation per MPH of tailwind. Keep in mind I'm talking about a bullet that takes 175 to 200 MOA to get from a 100 yard zero to 1000.
Then there are terrain effects. Some place like Oak Ridge, a headwind which ballistically should cause you to hit low, will cause you to hit 3/4 to a minute high due to the lift off of the berms/hill at 800 and 900.
Ned Ludd
Silver $$ Contributor
Under most circumstances, BC is an inherent property of the bullet. Headwinds/tailwinds can affect time of flight (lag time); effectively they affect velocity as the primary means by which they can alter trajectory. Typically, the effects are not huge as Wade pointed out.
It is far more common to observe dramatic elevation changes (POI) during pickups/letoffs in head-/tailwinds due to terrain features such as berms. These changes are extremely difficult to see; you will rarely ever see them in the mirage or flags unless the indicator you're looking at happens to be right on top of where the updraft/downdraft is occurring (which they almost never are). Because they can be very difficult to detect, your best bet is simply not to shoot during marked pickups/letoffs when you have strong head-/tailwinds. You can also look over the terrain features between you and the target to get some idea of how severe you might expect their effect to be (i.e. relatively flat versus really tall berms or large drop offs in between low berms). In addition to using the flags as potential windspeed indicators, you can usually detect the pickups/letoffs even when shooting prone via the wind on your legs or in your face.
It is far more common to observe dramatic elevation changes (POI) during pickups/letoffs in head-/tailwinds due to terrain features such as berms. These changes are extremely difficult to see; you will rarely ever see them in the mirage or flags unless the indicator you're looking at happens to be right on top of where the updraft/downdraft is occurring (which they almost never are). Because they can be very difficult to detect, your best bet is simply not to shoot during marked pickups/letoffs when you have strong head-/tailwinds. You can also look over the terrain features between you and the target to get some idea of how severe you might expect their effect to be (i.e. relatively flat versus really tall berms or large drop offs in between low berms). In addition to using the flags as potential windspeed indicators, you can usually detect the pickups/letoffs even when shooting prone via the wind on your legs or in your face.
I asked because I'm expecting some big tail and headwinds this weekend. When I plugged my load in to JBM, at a 0 mph wind from 180 degrees my drop was 21" less than when a 20mph wind was plugged in. That doesn't make sense. I read a blog on Bison ballistics that said it shouldn't be that dramatic http://bisonballistics.com/articles/why-headwinds-are-more-difficult-than-crosswinds but the angle of head and tailwinds effects the bullets more dramatically horizontally than a true crosswind. In 0 wind condition my load has shown on several occasions to have little vertical, when I see changes in that this weekend (not having shot much at 1k and never in strong head or tail winds) , I'd like to be prepared as much as possible to try and understand what's going on so that I don't drag my shiny new rifle all the way back to Mississippi behind the vehicle.
That is what I call a summer wind. 95% of our wind will be a tail wind during the summer.I have found you need a different tune from the point of aim . Head wind I like the tune to be above the point of aim. Summer below . Thanks to the use of a tuner It only takes a few shot to get it. . Larry
I asked because I'm expecting some big tail and headwinds this weekend. When I plugged my load in to JBM, at a 0 mph wind from 180 degrees my drop was 21" less than when a 20mph wind was plugged in. That doesn't make sense. I read a blog on Bison ballistics that said it shouldn't be that dramatic http://bisonballistics.com/articles/why-headwinds-are-more-difficult-than-crosswinds but the angle of head and tailwinds effects the bullets more dramatically horizontally than a true crosswind. In 0 wind condition my load has shown on several occasions to have little vertical, when I see changes in that this weekend (not having shot much at 1k and never in strong head or tail winds) , I'd like to be prepared as much as possible to try and understand what's going on so that I don't drag my shiny new rifle all the way back to Mississippi behind the vehicle.
I wouldn't worry about the wind at Bayou this weekend,i'm not ha ha ha I made a wind chart from 5-30mph with a 1/4,1/2,and full value wind I am thinking we will have a 1/4 value sse tail wind on Saturday and nne head wind on sunday.
Great article. This is exactly what we are going to get this weekend. Sunday will probably be worst but who knows.
You'll have plenty of sighters to get your vertical but the fish tailing winds are going to make for lots of dropped points
Unless you have worked with a tuner most don't realize the same load will have a tune both vertical up and down from the point of aim . Not uncommon for group to be 3/8 of a inch . Apart . Both will be in one hole but verticaly seperated . Like I said in a tail wind condition I like it to be a tune from the point of aim low . Larry
I don't know how to put it in a ballistic calculator or how much value a head or tail wind has. However, after 2 days of tail wind and 1 day of head wind it can and will push you up to dang near and 8 and down to dang near an 8. Saw it happen to f open and tr shooters all at the same time up and down the line from 284's to heavy bullet 308's.
Down South
FTR Junkie
We must have been at a different match or you need to wear your glasses, everyone i saw shooting never had a shot go above or below the 10 ring. Those "cup cake" conditions we shot in tend to keep the vertical tight........
Those cupcake conditions produced many waterline 6, 7, and 8's as wellWe must have been at a different match or you need to wear your glasses, everyone i saw shooting never had a shot go above or below the 10 ring. Those "cup cake" conditions we shot in tend to keep the vertical tight........
Ned Ludd
Silver $$ Contributor
But the real question in terms of ballistics is how much of that vertical was the direct result of the windspeed, and how much was the result of it hitting terrain features such as berms in between the shooter and the target. Unless the range is completely flat in the middle, the vertical is often caused more by changes in wind speed as it flows over the terrain. When the wind is flowing directly over berms and such in a direction parallel to the line of sight, missing a wind pickup will generally cause misses high (updraft), whereas missing a let-off will move the POI low (lack of updraft). Of course, that kind of vertical is easy to explain (especially for someone sitting at home that didn't have to shoot through it 
), but almost impossible to see. You guys shot very well indeed given the conditions!
), but almost impossible to see. You guys shot very well indeed given the conditions!You'd probably be close calculating the fps of the wind and adding or subtracting it from the muzzle velocity. Wind speed will seldom be constant to the target. For instance 10 mph is approximately 14.66 fps.
Don't forget, long rangers, wind above the line of sight is faster than in the line of sight. At the high point of 308 ammo headed to targets 1000 yards down range, the wind speed at it trajectory height can be 50% faster than in the line of sight. It varies with terrain; fastest in flat smooth ground (rifle ranges on the plains), lowest in the trees and other high obstructions.
Yes. Bullet BC is relative to the air it moves in. Just like muzzle velocity is relative to the barrel; higher fps numbers with a fixed barreled action, lower when shot off ones shoulder and the barrel's moving backwards while the bullet leaves.
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