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Down draft effects on bullet flight ?

 
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Old 10-24-2010, 10:19 PM
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Down draft effects on bullet flight ?

We were checking out some elk this evening and they were in my range but the guys I was with don't have the range so we put the sneak on them and the weather was awesome for seeing the air movement. It was a drizzle/snow and I could see the air rolling over a ridge and from the first spot I could see that a shot from that position would have gone through a huge harsh down draft but on our way up we got to a place where it looked like the bullet trajectory would have been under the down draft and only had to contend with a cross wind.
Any way the guy with the first shot FAILED to drop the lead cow so the we didn't have a shot on any of the 6 brow tine bulls, I really wish I would have shot from position 2 cause it was 836yrds to the largest 6 point standing there begging me to shoot, heck we stood there getting our act together for five minutes and he stood there, should have got greedy and shot!

So I was thinking about shooting through that down draft and it's affect on ballistics of that bullet, I was wondering if say the cross wind looked like 10mph cross but there is an equal looking down draft could you add that cross wind value to the elevation adjustment, wouldn't the wind deflect the bullet down at the same rate as it would with an equal cross wind? Any thoughts on down drafts or up draft?
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Old 10-24-2010, 11:10 PM
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Re: Down draft effects on bullet flight ?

Quote:
Originally Posted by bigngreen View Post
We were checking out some elk this evening and they were in my range but the guys I was with don't have the range so we put the sneak on them and the weather was awesome for seeing the air movement. It was a drizzle/snow and I could see the air rolling over a ridge and from the first spot I could see that a shot from that position would have gone through a huge harsh down draft but on our way up we got to a place where it looked like the bullet trajectory would have been under the down draft and only had to contend with a cross wind.
Any way the guy with the first shot FAILED to drop the lead cow so the we didn't have a shot on any of the 6 brow tine bulls, I really wish I would have shot from position 2 cause it was 836yrds to the largest 6 point standing there begging me to shoot, heck we stood there getting our act together for five minutes and he stood there, should have got greedy and shot!

So I was thinking about shooting through that down draft and it's affect on ballistics of that bullet, I was wondering if say the cross wind looked like 10mph cross but there is an equal looking down draft could you add that cross wind value to the elevation adjustment, wouldn't the wind deflect the bullet down at the same rate as it would with an equal cross wind? Any thoughts on down drafts or up draft?
Interesting question !

I would think that you would add the downdraft value (If 10 MPH it would be the same effect
as a cross wind at that distance) Plus the drop for the distance and come up with a total drop
that you would have to compensate for.

It would be the same as a 10 mph head wind plus the drop for a total elevation change.

J E CUSTOM
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Old 10-24-2010, 11:21 PM
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Re: Down draft effects on bullet flight ?

I've contemplated the same things recently, but all of my shooting is done in relatively flat country; so I haven't thought alot about it.

The old Sierra program I've got has a spot for vertical winds, and definately changes the impact with an input in that box.

Using the 338 Edge as an example, I punched in 10 mph vertical and a minus 10 mph vertical.......suprisingly, it showed a difference in drop of 25" either way from no wind at all at 850 yds!! This was nearly the amount of a 10 mph true crosswind according to the program.

I would think that vertical winds and up/down drafts happen frequently in steep mountain shooting. I would also think that the shooter would need to figure how much of the total wind is acting vertical vs horizontal and apply both corrections simultaniously.

I can imagine shooting down hill, parallel and along the apex of a ridge, with a wind blowing from the right and behind. It seems perfectly reasonable that the wind would actually "lift" the bullet and try to push it away from the ridgeline, counteracting gravity. Between shooting down hill and the artificial lift, I can imagine shooting way high. Not to mention the crosswind effect because the wind is trying to "turn around" the ridge too!!......Wow, way too much thinking involved!!

Good selling point for the old Sierra program on a PDA. I haven't found anyplace to input any kind of vertical winds in the Nightforce program. I don't know if the newer Sierra stuff has that box or not?
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Old 10-24-2010, 11:48 PM
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Re: Down draft effects on bullet flight ?

Very interesting that there is a program out there that actually has that function, this particular spot is a spot we kill a lot of elk of so I was really watching how the wind moved. We can drive the truck up to 1100yrd and they don't even know it and we can shoot from that point once the 338's are up and running. This spot is a east and west face that is bowl shaped with a sharp ridge on the south side which is on the prevailing wind side, I could see the wind would roll over the top with a harsh down draft but there was almost no wind near the ground so moving up to the base of the bowl I had 836yrds and I think the down draft was cut of by a cross wind. Still kicking myself for not shooting that bull, he was only about 260-270 class but had a bottom half of a 380+bull and a top half of a wiener like he ran out of grub half way though growing. I will shoot an elk in that spot so I really want to figure it out!!

Another note on this spot is that the south face is open sage brush and I think the south wind hits it and starts rolling up the face and then whips over the top, maybe something to think about as I shoot a lot of spots that are open on the south side and the elk hang just of the north sides and the air is dead in there so if I don't have to pitch it up to high I can stay in the dead air.
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  #5  
Old 10-25-2010, 02:18 PM
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Re: Down draft effects on bullet flight ?

Shawn Carlock wrote about this in his article on reading the wind, have a look for it, it is an excellent articel.
Basically as JE Custom said treat it as a side wind, wind speed and direction and then add it to the elevation needed.

Stu.
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