Range Report Vertical dispersion from terrain/wind

[vman]

Hi guys.

I have been getting a little mid range (550-600) yard shooting in lately at my local range and Im amazed at the difficulty of achieving good results at this distance. The range does not go any further and backs onto a steep cliff face.

Im shooting handloads, that are giving me low ES/SD and on many occasions I have shot groups of less than 1" at 300 and 400 yards. Im 100% confident that my handloads are shooting better than any factory round available, so Im blaming the indian and not the arrow.

From about 400 yards to 600 yards the terrain gets steeper as the cliff bottom begins. Im also aware of the slight angle this forces, however I have taken everything into equation.

Considering my handloads give me wonderful tight verticals at 400, im wondering why when I move out to 550-600 i suddenly start to see random vertical (sometimes off the paper). Is it possible that winds approaching the cliff might lift or drop the bullet a significant amount?

I would really love to master 600 yards so that i can begin F class running and eventually move onto 1000 yard F Class comps.

If you have any experience/knowledge that you believe would help ol vman out in this situation it would be much appreciated.

 

[mattj]

Re: Vertical dispersion from terrain/wind

Shawn Carlock wrote an article that includes a method for guesstimating vertical due to wind over major terrain features. I have it bookmarked -- link isn't working for me right now, but maybe it will work for you / work later:

http://www.longrangehunting.com/articles/reading-wind.php

 

[vman]

Re: Vertical dispersion from terrain/wind

not working... server may be down

 

[jbailey]

Re: Vertical dispersion from terrain/wind

(1) do you have a picture of the terrain? photo worth a thousand words...
(2) are there wind flags out there? If not, you might want to ask the club if you can post some - nothing huge, just streamers that give you idea of the conditions down range.
(3) what wind model are you using to estimate wind? I use a NEAR, MID and FAR model that estimates wind speed and vector at each, then averages the three for an overall value to dope into scope.
(4) because wind conditions continually change, you should do your wind model for the most likely wind conditions - i.e. not during a lull or a gust. You also need to continually check the major wind condition and change your wind model if the major condition changes. Finally, hold off shooting until you are shooting in the wind conditions your model is built on.
(5) because there is a lot to do, it helps if you have a spotter that can continually be evaluating wind conditions, as the shooter focuses on the fundamentals of marksmanship - good trigger pull, breathing, sight picture, position, etc.
(6) what caliber are you shooting? Its not running out of steam past 500? Barrel isn't over-twisting the bullets, inducing a lot of spin drift?

 

[notquiteright]

Re: Vertical dispersion from terrain/wind

I shoot at least 600 yards alot. I do it over alot of rough terrain. I do it over manicured lawn. I do it on a plane, I do it on a train....ooops.

Anyway while all things are possible I really dont notice verticle displacement as rather strong winds tear across ravines and hillocks. The worse is at a 'range' where a steep bluff of about 10' sits at 500 yards. But even that takes winds above 15mph to see any verticle I cant log as me.

I log each shot as well as a comment if I did something stoopid. Most the time its a failure to set the rear bag solid and attempting to muscle a round into the 10 ring.

You sound as if you are just starting to shoot 600 yards. It has been my experience that what you are able to do at 300 doesnt hold true at 600. It doesnt take much to make a huge difference in your verticle. Attention to every detail of your postion and how well you build your rifle's support counts.

And I mean EVERY.

What I must have missed is the horizonal displacement. Were you able to dope the wind well enough to stay within a 10 ring so it was just verticle that was funking up your day?

Was the displacement very consistent? I mean always high or low? (This is why logging each shot is helpful)

See what your logbook says about any trend. It will help.

 

[jagged77]

Re: Vertical dispersion from terrain/wind

Vman, my range set up is quite similar to yours. We have 500 yards max range and beyond the backstop there is a steep quarry / cliff face (see below pic taken at the 200 yard firing point).

The range itself is situated high up on the hills bordering the Pennines and open moorland, hence its always windy.
Usually the wind comes full value from 3 o clock, shooting in these conditions is usually a straight forward exercise of watching the flags. However sometimes the wind shifts to come head on (or in the 10 o clock to 2 o clock direction) then strange things can start to happen vertically with the bullet. Also vertical shift can happen when the wind comes from behind.

I'm sure there's all sorts of things going on with the air flow around the cliff face and backstops that the wind flags just don't show, hence some puzzling scores occasionally. Its not just me that's witnessed it either, there are guys shooting custom 6.5 x 284's that are more than capable of scoring possibles that have suffered from it too.

Only thing to do is watch the wind conditions and flags and keep gaining experience, not all ranges will be alike and most likely be easier for you having learnt / practised on a tricky one.

 

[vman]

Re: Vertical dispersion from terrain/wind

View from the 550 Yard line to the benches

Thanks for the input guys. Much appreciated.

Im deffinately going to start putting flags out there.

 

[jbailey]

Re: Vertical dispersion from terrain/wind

Vman and Jagged77-
Very cool to see the terrain on your ranges. Very different than mine:

http://i342.photobucket.com/albums/o436/mtgrizzard/CVT0011.jpg
and
http://www.quanticoshootingclub.com/ranges-range4.php

Vman-
there looks like some good wind indicators out there at 550. All those trees/brush behind targets are perfect. Remember that the wind at the target will have the least impact on the bullet, because even a big gust will only move the bullet a tiny bit. Wind at the shooting location will have the biggest impact. Also, remember about wind gradients - wind is stronger the higher the bullet is off the ground, so the mid wind conditions are also very important.

If you don't have a tactile and visual wind speed indicator list, here are some that I use and have had good luck with:

Wind Speed Tactile and Visual Indicators
0-1 MPH Wind imperceptible
No grass or leaf movement
Smoke rises straight up
Mirage runs vertical

1-2 MPH Cooling effect of wind may be noticed
Light movement of grasses
Only a few leaves on any given tree in motion
Mirage begins to lean to 12:30

3 MPH Wind pressure can be felt on bare arms
Grasses obviously in motion
All leaves on any given tree in light motion
Mirage leans to 1:00-1:30

4 MPH Wind pressure can be felt on face
Small twigs bearing leaf clusters begin light motion
Mirage leans to 1:30-2:00

5 MPH Tips of smaller branches begin motion
Mirage leans to 2:00-2:15

6 MPH Tips of branches begin motion
Mirage leans to 2:15-2:30

7 MPH Larger (trunk) limbs begin motion
Young (softer) leaves begin to flip over on windy side of trees
Mirage leans to 2:30

8 MPH Tree tops are in light motion
Mature leaves flip over on windy side of trees
Mirage leans to 2:45

9 MPH Tree tops show obvious movement
Mature leaves flip over on windy side of trees
Mirage leans to 2:45-3:00 and begins to run

10 MPH Wind pressure can be felt against the body
Tree tops show substantial movement
Mirage runs slowly and parallel to ground

11 MPH Mirage runs quickly along the ground, begins to break up

12 MPH Wind pressure can be felt against the body
Mirage runs very quickly in sheltered places, mostly broken up in exposed areas

12-15 MPH Dust is raised
Lighter debris moves around
Mirage blows off completely in exposed areas

15-20 MPH Dust clouds blow around
Debris blows around
Smaller tree trunks sway
Major limbs on larger trees in constant motion

20+ MPH Difficulty walking
Larger tree trunks sway

 

[vman]

Re: Vertical dispersion from terrain/wind

Thanks for the info James

Has anyone come across any good reading material that covers terrain AND wind?

I understand that this is the most difficult variable a shooter will face, and I do all that I can to train myself for it but I understand that time, practice and experience are key factors other than superior ballistics.

Besides my eagerness to hit the ground running with competitions im also an avid hunter... the first shot needs to count for ethical reasons.

This weekend I will break out the wind flags and 4500NV.

 

[jbailey]

Re: Vertical dispersion from terrain/wind

Vman-
A few of the FM and TM of the US Armed Forces has some discussion of terrain and it's impact on wind. Terrain varies so much, as does wind (literally changing every second). I think however you will be better served by getting out there with your wind flags, your rifle and a data book. Carefully shoot each round after evaluating wind and log conditions and results in the data book. Take the data book home and after a few range sessions, you will have a better read than anything you will get out of a book.
Report back here and let us know your progress!

 

[sinister]

Re: Vertical dispersion from terrain/wind

You don't need big, formal range wind flags. You can get some plain stakes and fluorescent surveyor's tape from Home Depot or Lowe's and put those out every few hundred yards (benchrester style) to help give wind speed and direction indicators.

If you don't want to trash up the place just tie tape to limbs or fences.

-One of the better see-it-to believe-it demonstrations at basic sniper schools if there is any wind is to set off smoke pots (think smoke grenade except paint can size) every 200 or 300 yards downrange and watch what happens. You will see how the wind carries the smoke across open spaces, around hills, humps, hillocks, and trees or any other folds in the ground.

It is impressive watching smoke swirl around or over the tops of structures and see how winds are not uniform as they circulate around sharp edges like walls, roofs, and automobiles.