Horizontal Impact Difting Help

[GrayGhost]

Same range, same conditions, same day,groups.

100 yards centered well.
200 yards a inch right.
300 yards a good 2" right.

The range is lined with tree's well. Wind minimum, light snowfall appeared to fall at about maybe 5 o'clock or less lat time. Also I shoot this range often and it is always there centered at 100 yards groups move right at 300. What little wind there is, would be left to right.

I am not sure if this is rifle cant, scope cant, wind or myself and technique. Puzzling ?

* 22-250, ballistics show 4.7" / 5 mph wind / 300 yards for my ammo.
* 2 pound trigger
* right handed
* caldwell front and rear bags on well built wood bench. no front rest.
* rifle and scope about 10 pounds.
* reticule appears plum
* 50 grain v-max

What do you think it is ? I suppose it is likely wind although the wind seems absent. Also this is regular on many, many days. I practice my shooing technique, cold fire trigger pull, etc. regularly. I am just not sure what is doing this ? The covered bench area is a bit more open and I could be getting a puff of wind at the muzzle their I suppose. Yet, something tells me it may be mechanical or technique related.

Thank you much for your time and thoughts.

 

[oldjad01]

I am not an expert but if the bbl and the scope are not in line, one above the other, then you would have only one range where they would be right on. I have no idea how to correct it unless the base is the problem. You don't mention which bases, and did the action come from the factory with the scope mount holes drilled or were they added later? Hope this helps. JimDee

 

[Forum Boss]

First, you may be getting stronger crosswinds down-range than in the first 100 yards. That alone can account for increased windage at 200 or 300 yards.

Also, remember that, as a general rule of thumb, wind drift increases with the square of the distance.

So, if you had 1/4" drift at 100 yards,barely measurable) you would have 1/4" mutiplied by,2x2) or 1" drift at 200 yards.

You would have 1/4" mutiplied by,3x3) or 2.25" drift at 300 yards. Interesting how that nearly matches your numbers, eh?

This "Rule of the Square" is good for rough estimates. You'll have to consult a ballistics program for the fine details. See: http://www.6mmbr.com/ballistics.html

See: http://www.6mmbr.com/Winddrift.html

What this suggests to me is that nothing is wrong at all, but you're just not noticing the effect of the wind at 100 yards because it's very small relative to your group size.

 

[GrayGhost]

Very interesting articles well written as always. I am sure that is it, I am underestimating what I consider little to no wind. Further proof, I typically will be 1/4" right at 100. If I shoot a 5 x 5 @ 100 it shows.

I enjoy math,although a math teacher I am not). Here's a thought.

If typically it takes 200 or even 300 yards in some calibers for this drift to show in a very light wind. How would you calculate from there ? It appears you may have to convert back to 100 yards first and then say,6 x 6 for calculating drift at 600 yards) But first back to 100 if you shot at 200 or 300 noticed drift and wanted to calculate 600 yards. Does that sound correct ? There may be a multiple there but, I did not find it. It would be handy to know how to calculate from 200 & 300 rather than 100.

Also, although close this does not match my ballistics from a program,program may not have been accurate ? ).

Mine shows .5" @ 100 yards in a 90 degree 5 mph wind. It then shows the drift at 600 to be 23" for the same. If I do the 6 x 6 method I get 18", .5 x 6 = 3 / x 6 = 18" ) A difference of 5" @ 600.

I tend to enjoy the math aspects of rifle shooting,not a whiz though) along with techniques,styles,trigger pull,etc) of shooting more so than custom rifle talk. Probably because it does not cost anything for me to improve this way,grin).

This statement in the article "for distance shooting wind judgment is more important than whether your rifle shoots .2 moa or 1 moa" Really says a lot.

I really enjoy this kind of stuff. Maybe someone on here can show how to calculate from 200 and 300 yards, where the drift first shows up.

 

[Forum Boss]

You've got the hang of it. The "Rule of the Square method" still applies, but becomes less exact at longer distances for a lot of reasons. First, the bullet is slowing down so flight time per yard traveled increases. Second, as the bullet slows down the BC,in most cases) will change.,Sierra notes this in their BC calculations; other bullet makers do not). Ambient pressure/temp/altitude can have an effect too.

So how accurate would the Rule of the Square be at 600 yards?

Using a Pejsa Ballistics table, with a Rem 260 shooting a 139 Scenar, it calculates wind drift at 0.24 MOA, with a 5 mph, 9 o'clock crosswind. 0.24 MOA, at 100 yards is 0.258",1 MOA = 1.074" at 100 yards).

The program says drift at 600 yards is 1.66" MOA. That equals 10.7".

Other programs may give slightly different values.

Using a Rule of Square method, we'd have 0.258 multiplied by,6x6). That equals 9.29". So you're off by about an inch and a half, or about .25 MOA at 600 yards.

This jives with results I've seen from the Sierra ballistics program--that you get about 1/4 MOA error at 500-600 yards and it grows from there. But, as a rule of thumb, squaring the distance factor and multiplying by the 100-yard wind drift will get you close.

I don't know what ballistics program you are using. I think it may be overcorrecting.

 

[GrayGhost]

Pretty darn close and quick with a pocket calculator. I do need to change programs though.

But still, one needs to convert to 100 yards if shooting at 200 or 300 right ?

At 200 can you just divide by 4 ? Not sure what one would divide by at 300 ?

But, I think you can divide by 4 at 200 to get the 100.:comp: Then do the 6x6 if you wanted to shoot say 600 with your next round/group. :idea:

 

[Forum Boss]

Yes I do think its better to use 100-yard drift as a baseline. In your example, divide the 200-yard observed drift by four to get a 100-yard baseline. Then,

multiply by 9 for 300 yards
multiply by 16 for 400 yards
multiply by 25 for 500 yards etc.

As noted, the results won't be perfect,it's best to use an actual ballistics program), but you'll be close. Out past 700 yards, because of the bullet slow-down/shifting BC effects, the Rule of the Square underestimates actual wind drift more dramatically.

Ideally, for long distances, you'll prepare your own set of come-up and windage tables based on the calculations of a good ballistics program supplemented by observed results.

 

[gcabrera]

I love this site, but this is the first time I venture to post a response.

Regarding the wind drift, if you know how your rifle/caliber/load behaves at 200y, and you know that under a given condition the bullet will move so many inches to the right or left, I would make the following mental calculation:

For 300Y -->,3/2)x,3/2)= 1.5 x 1.5 = 2.25X the drift experienced at 200Y
For 400Y -->,4/2)x,4/2)= 2 x 2 = 4X the drift experienced at 200Y
And soon on.
For instance, at 600Y
,6/2)x,6/2)= 3 x 3 = 9X the drift experienced at 200Y.

I agree that having a good feel for wind drift at 200Y or 300Y, as baselines, is very practical, in order to guess a hold off for longer shots.

Regards to all,

George

 

[Forum Boss]

George, that's a real smart way to do it, particularly since it is sometimes hard to gauge the actual drift at 100 yards.

Say you have a rock-solid windless zero for two hundred, and you see you are being blown 1" right. Since 600 yards is 3x the distance, using the Rule of the Square, you know you're going to be about 1" mutiplied by,3x3). So, that puts you 9" right at 600 yards.

Again, this isn't exact. A ballistics table will probably show your Rule of Square estimate is off by .25-.35 moa, but your estimate will keep you fairly centered on target and then you can add/delete a click or two.