Fine Tuning @ 1300

[jackem]

I'm new to all this and have new equipment that I'm attempting to get working together. I have a 338LM, a G7 NF scope, and a B7 LRF. I still using factory HSM 300 gr VLDs, reloading is this winter's project...

Previously I was hitting consistently 2 - 3 feet high at 1300 yards so I adjusted the muzzle velocity in the G7 to correct, of course I first reduced muzzle velocity just to confuse myself, and ended up adjusting the FPS from 2780 to 2840 once I figured out the correct direction of adjustment.

With the light going fast and the wind going from a measured nothing to 5 mph I fired the last 3 rounds. Obviously I did not read the breeze correctly with a horizontal spread of 18". But the vertical spread, including the third shot in the dirt beside the plate, was about 6''.

I believe I can get the yardage, dial in a correction and be very close vertically. However, with winds 0 - 5 which is about as good of conditions as one can hope for, I was disappointed in the horizontal spread. I was shooting prone with bipods.

Any suggestions or pointers?

 

[M67]

At 1170m 18" or worse, horizontal is what you get if you are not on top of what the wind does. On can, certainly with the 338LM, shoot much better than that - But then you better watch the wind, near, far and in between.

K

 

[jackem]

Truth is I was really happy to have the elevation dialed in close enough for hits and didn't pay enough attention to the wind.

However, feeling/seeing the difference of less than 5 mph wind, while getting the shot off is gonna be a challenge for me I think...

 

[M67]

a challenge

Yep, wouldnt be much fair if if it was different for you.
K

 

[jackem]

Yep, wouldnt be much fair if if it was different for you.
K

True. I'm wondering if a 0-5 wind was enough to cause that big of a horizontal spread? I suspect its not and if wind and the shooter are all that control horizontal spread(?) then something I'm doing or not doing is effecting the spread.

Any known bad habits cause horizontal spread much more than vertical spread?

Other than fast foods, of course...

 

[Broz]

The difference between zero wind and a 5 mph full value wind at 1300 yards would be about 1.4 moa. Or roughly 19". Then if you have a combined accuracy of 3/4 moa between the rifle, ammo and shooter skill you need to add that in too. So in reality if you are just getting started at this you did pretty good I feel. I would look at the distance of error from your pont of aim. Not group size. I strive to get as close to point of aim as possible no matter what side of it I am on. This is why I choose the crease behind the shoulder for point of aim. It offers me the widest kill zone and as you see width is tough with any wind at all. There is always wind somewhere durring the flight path.

Another thought I have is, were you able to split that circle aiming point with your cross hairs? Is the plate about 20" across?? The dot 2"?? If the crosshair subtension of your scope reticle is covering the dot completely it will induce a small amount of error too.

Lastly f you have not read this I think it is worth your time.
http://www.longrangehunting.com/forums/f116/importance-being-solid-91149/

You can not be to solid on your set up.

Jeff

 

[jackem]

The difference between zero wind and a 5 mph full value wind at 1300 yards would be about 1.4 moa. Or roughly 19". Then if you have a combined accuracy of 3/4 moa between the rifle, ammo and shooter skill you need to add that in too. So in reality if you are just getting started at this you did pretty good I feel. I would look at the distance of error from your pont of aim. Not group size. I strive to get as close to point of aim as possible no matter what side of it I am on. This is why I choose the crease behind the shoulder for point of aim. It offers me the widest kill zone and as you see width is tough with any wind at all. There is always wind somewhere durring the flight path.

Another thought I have is, were you able to split that circle aiming point with your cross hairs? Is the plate about 20" across?? The dot 2"?? If the crosshair subtension of your scope reticle is covering the dot completely it will induce a small amount of error too.

Lastly f you have not read this I think it is worth your time.
http://www.longrangehunting.com/forums/f116/importance-being-solid-91149/

You can not be to solid on your set up.

Jeff

Jeff, I'm sure all of us appreciate your input, I know I do. I have read the importance of being solid and you're right my set up wasn't 100%. I was using harris bipods and a rear bag on top of a large old cotton canvass, talcum powder dust there...

I believe the plate is about 2 feet wide with the dot 3'' to 4'', I'll measure the next time out. I can see enough of the dot with my cross hairs on it so I should be able to work on reducing that error.

I had 2.25 MOA dialed in for windage, the correction my B7 gave for 5mph at 1312 yards. Do you think that was too much?

Thanks for the advise about POA on game. One weekend left of bear season and then a bull and a cow tag to fill next month. The more of the bullet's 'pre-flight checklist' I can check off before the shot the more likely the freezer will fill up.

Jack

 

[Broz]

I had 2.25 MOA dialed in for windage, the correction my B7 gave for 5mph at 1312 yards. Do you think that was too much?

Jack, my 338 LM with a 300 OTM, MV of 2800 shooting at roughly 4000 ft altitude is ike this.

5 mph full value wind at 9:00 or a left wind. the correction would be .8 moa left for spin drift and adding 5 mph left wind a total of 3.5 moa left correction.

The same shot with a 5 mph right wind from 3:00 would be a total correction of 2 moa left.

It gets a little confusing adding or subtracting spin drift . But your right twist barrel will have a SD correction of over 10" left at 1300 yards.


Jeff

 

[jackem]

Jeff,

Thanks for your time. I think I understand the SD effect now that I read a bit on it, I had not considered it before.

So, if I have a 9 o'clock 5 mph wind I should add .8 MOA to the correction for the windage the B7 gives no matter the distance -and subtract .8 MOA for a 3 o'clock wind?

And would the correction double in a 10 mph wind?

Thanks again,

Jack

 

[Broz]

Jeff,


So, if I have a 9 o'clock 5 mph wind I should add .8 MOA to the correction for the windage the B7 gives no matter the distance -and subtract .8 MOA for a 3 o'clock wind?

And would the correction double in a 10 mph wind?

Thanks again,

Jack

No SD is relevant to distance. That .8 was for a 1300 yards shot with your rifle. It would only be .5 moa at 1000 yds

Since your rifle has a right twist barrel you will have right spin drift. So the correction for the SD will always be a left correction and is completely seperate from wind drift.

My ballistic calculator has the option to always correct for SD and I leave it on all the time. So it always adds or subracts it from my shooting solution it gives me when I enter all field conditions and distance.

Jeff

 

[jackem]

As soon as I can get set up for reloading and can stop shooting these tightly wrapped $5 dollar bills I need to shoot enough to develop a correction chart for shots beyond a 1,000.

For now I'll use a politically correct adjustment;
Be liberal when adjusting for winds from the left
Be conservative when adjusting for winds from the right...

Jeff, Thanks for your patience!

Jack

 

[COBrad]

I've been using that G7 rangefinder this year. With careful fine tuning I have found no need to develop a chart for shots over 1000 yards. Mine was giving me dead accurate ballistic solutions out to 1380 yards last weekend. What I failed to add was the extra click in windage for spin drift at that range. I have my LR scopes zeroed .5 MOA left and that compensates nicely for spin drift out to 1K.
That shifty 5 mph wind at 1300 is real challenging, especially if it switches directions as well. I shoot marmots a lot in above-timberline basins. The winds are usually pretty shifty when they pick up. Last weekend they were not only gusting 0-5, but shifting frequently in direction. I am still learning to read the wind, so I was hitting a half MOA on one side, then again to the other side. Very frustrating. I squeezed one off during a momentary lull and hit the edge of a tennis ball sized target. It was a good one to quit on, so I packed up and went home.

 

[mike33]

No SD is relevant to distance. That .8 was for a 1300 yards shot with your rifle. It would only be .5 moa at 1000 yds

Since your rifle has a right twist barrel you will have right spin drift. So the correction for the SD will always be a left correction and is completely seperate from wind drift.

My ballistic calculator has the option to always correct for SD and I leave it on all the time. So it always adds or subracts it from my shooting solution it gives me when I enter all field conditions and distance.

Jeff

Jeff i couldnt agree more on spin drift. I was shooting yesterday with some buddys that is going with me to Co, this year. They shot at 500 than 800 and stopped with there euiptment. I broke out my edge at 1220 yards. My first shot at a jug was high due to i used drop chart for 1400' and was shooting at 2550'. I dialed down 3/4 moa elevation fine. I left othere shoot and they held 2 moa for wind and was still off around a 4-5 mph wind. I got up and held almost 3 moa and hit the jug. I told them rhand twist its going right have to allow for that besides the wind. I have never seen spin drift discussed to much but i have sure learned what it can do.
MIke

 

[T3-OleMan]

Jack, my 338 LM with a 300 OTM, MV of 2800 shooting at roughly 4000 ft altitude is ike this.

5 mph full value wind at 9:00 or a left wind. the correction would be .8 moa left for spin drift and adding 5 mph left wind a total of 3.5 moa left correction.

The same shot with a 5 mph right wind from 3:00 would be a total correction of 2 moa left.

It gets a little confusing adding or subtracting spin drift . But your right twist barrel will have a SD correction of over 10" left at 1300 yards.


Jeff

Jeff, where can I go get my spin drift data for my 338WM (24 3/8" 1/10"R) 185gr GMX, MV 3,009 @ 9,928'....in the snow-no wind {:>)? Don't do moa's Zeiss Victory Diavari 4-16x50 T* FL 30mm and run their in house Reticle analysis to get "Optimum Power so my Rapid Z 800 will be right on for drop chart for temp - alt. and MV changes. What would be my "SD correction of over X" left at 800, 900 & 1,001 yards"? Please forgive the underrange-some times you have to go where the preacher is.