Spin drift question

[desert deuce]

Hypothetical, theoretical, practical, what if.............You have one rifle, one load.

You are at a Creedmoor Match where you will shoot, 200, 300, 500, 600, 800, 900 & 1,000 yards over the span of several days.

Your rifle is affixed with a wind gauge front sight and you know with the rear soule set on zero and the front sight set on zero the rifle, load shoots point of aim at 100 yards.

You have Applied Ballistics Web Calculator for your rifle load for those distances.

Now we know the right twist rises in a right wind and falls in a left wind. Does this affect the wind drift setting at any distance since wind drift is calculated without a wind direction or intensity?

At what distance is the point of diminishing returns reached?

[bruce m]

zack,
thinking "deflection" rather than "drift" helps your thinking here.
the bullet is "deflected" by the wind.
2 aspects of the wind affect deflection, speed and direction.
deflection varies proportional to speed, e.g. double the speed = double the deflection.
for a given speed, max deflection is at 3.00 and 9.00 o'clock.
using the rhs of the clock only 1.00 and 5.00 o'clock is 1/2 of 3.00 o'clock.
2.00 and 4.00 is not exactly 3/4, but close to.
elevation changes occur as you say as well.
my own rule of thumb is 1 moa per elevation per 10 moa windage required on the sight.
because i have to shoot as an individual and read my own wind, i use each 100 increment of range as a multiplier, and although this is incorrect it is not far from what is required.
if anyone is interested i can discuss a formula i use, which is quite quick if you practise it.
it includes range speed and direction.
bruce.

[gunlaker]

About three this morning I realized that I'd made a big mistake in my post. The angle the rifle canted with the bubble on the edge of the line was about 2 degrees not two minutes. Sorry for the error.

Chris.

[gunlaker]

Hypothetical, theoretical, practical, what if.............You have one rifle, one load.

You are at a Creedmoor Match where you will shoot, 200, 300, 500, 600, 800, 900 & 1,000 yards over the span of several days.

Your rifle is affixed with a wind gauge front sight and you know with the rear soule set on zero and the front sight set on zero the rifle, load shoots point of aim at 100 yards.

You have Applied Ballistics Web Calculator for your rifle load for those distances.

Now we know the right twist rises in a right wind and falls in a left wind. Does this affect the wind drift setting at any distance since wind drift is calculated without a wind direction or intensity?

At what distance is the point of diminishing returns reached?

I think the point of diminishing returns is reached almost immediately .

However I still believe that understanding the basic principles allows you to get the situation under control faster when strange things start happening. Like trying to keep roughly centered on the target when you realize that your zero is off a little from where you thought it was, and the wind just reversed.

Chris.

[desert deuce]

Obviously the definitive solution to these questions demand Gunlaker and Bruce M be confined to the same range together indefinitely to work out the answers, achieve agreement and outline a best practices going forward. We would all benefit from the results should they choose to share the information. (Perhaps we are fortunate they are located at the opposite ends of the earth.)

However, in doing so we may create a monster that could/should realistically break all standing records.

Case in point was recently demonstrated at Byers Long Range Matches (you will have to look at the scores yourself) wherein the "experienced" shooter/spotters posted some impressive scores in less than favorable conditions. The key here, I am intentionally belaboring the point, I think the key is taking the available information to the range and learning how to apply what you know to what you see and achieve a desired result on the target, understanding that the conditions are in control and you will not be 100% successful at perfection.

Perhaps the secret is to accept the conditions and work with them. Success measured at 100% will likely fall short but the riflemen that shoot matches and practice will likely score among the top four at any match. Which obviously means one of the four will win the match.

The fly in the ointment, so to speak, is the mental aspect. Can't help you with that one but please let me know if you get it figured out.

[bpcr shooter]

personally I dont think "we" can have a one size fits all for this problem. Do PP bullets not drift as much? does adding GG's to the bullet better or worse for drift? does depth of those grooves make it better or worse?? does depth of grooves from your rifling make a difference? I would think there are just way too many variables to say....put 3min in the sight ad send it, it should be there. That and is there a range that has flags high enough for us to see that wind isn't affecting it??

just some thoughts......matt

[bruce m]

zack,
you have rpreviously stated that you put 2moa on your foresight prior to shooting long range.
for a 200 zero, this would be about right for long range to deal with spindrift.
matt.
spindrift is not affected by grease grooves or lack thereof.
it is quite calculateable.
it is due to the yaw of repose of the bullet.
who wants a deadwind zero halfway between the centre and the edge of the target?
bruce.

[Distant Thunder]

bruce,

are you sayin that 1 degree of tang sight cant is about correct for 1000 yards shooting?

[bruce m]

jim,
i believe that the angle of the staff should be such that the aperture should be roughly 3/10 of 1 thou to the left of where it is at a very close range zero.
2/10 of 1 thou to the left of a 200 m dead wind zero.
i call 1/10 of 1 thou 1 point to differentiate between that and 1 moa, in case sight radius causes 1 point to differ from a moa..
my self i prefer to have the staff verticle and put the spindrift on the windage foresight because it is easier for a lay person.
if using a fixed foresight, i would drift it in the dovetail to achieve a dead wind zero for 900 yd in a long range only rifle, as this is an average of 800, 900, and 1000.
going on the foresight rings you have made me over the years, you are far more qualified to establish the staff angle than i
i have in my possesion a raton wind flag to compare with our wind flags here in oz, and its angle of lift etc is very similar to ours.
getting back to establishing a dead wind zero, it sounds simpler than it is.
i now do it at 50 yds if possible, as there is less wind effect on the bullet there.
then adjust the sight to allow for spindrift before going to long range.
i do remember dan theodore explaining how he used spirit levels to allow for cant of the staff.
maybe someone has his writing about this stored somewhere?
bruce.

[bruce m]

i am having a mental blank.
1/10 of 1 thou might be wrong, but i don't have time to get it established.
bruce.

[beltfed]

I wish I could remember what Dan T had suggested for thickness of a shim
under the right side of the tang sight base to allow for spin drift.
I believe it was somewhere between 0.002 and 0.004"
beltfed/arnie

[semtav]

viewtopic.php?t=23662

Some of his posts about spin drift are here

[desert deuce]

Bruce M wrote: zack,
you have rpreviously stated that you put 2moa on your foresight prior to shooting long range.
for a 200 zero, this would be about right for long range to deal with spindrift.

Yes and no Bruce. Yes, that is what I did, no that has been modified slightly which means I don't exactly do that anymore.... If it was anybody but you and Gunlaker I probably would not go to the trouble to explain what I have encountered. Of course there is Steve 1 and Steve 2 but I have already explained this to them as well as Cliff Gregg, more or less.

The best summary I can offer is theory collided with reality and I adjusted to reality. Right this instant I am not remembering the numbers, but, here is what I do now with each long range rifle.

I do the set up of the rear soule as Dan T advised with magnetic level then shim the sight base to make that introduced cant permanent. Used an aluminum Coca Cola can to make the shim on the latest one. (See Dan's email to Bruce M 10/10/2009)

Then I take my long range load and rifle to the range and zero the front wind gauge and rear soule and then move the front sight base until the bullet strikes dead center at 100 yards while both front and rear sights are on zero.

Using a 2'x4' piece of cardboard I put the aiming point at the bottom center. I lay a one inch blue painters tape line straight up the middle to off the cardboard. Then using a plumb bob I set the top of the tape at the edge of the cardboard plumb with the aiming point below. From the center of the aiming point below I measure up 34" and mark that spot.

Go back to the bench and very carefully raise the elevation until the bullet strikes the 34" mark on the blue tape. Note, the vertical leg on the aperture front sight helps plumb the sight to target on the tape.

I then adjust the front wind gauge knob until the bullet strikes 1.5 inches to the left of the center of the blue tape 34" above the aiming point.

Understand now, this is what I do now and it is subject to change if something better is discovered.

[bruce m]

zack,
i was going to say that you and i have a lot in common, but now i think you are further out there than i am.
bruce.

[bruce m]

jim,
i believe that the angle of the staff should be such that the aperture should be roughly 3/10 of 1 thou to the left of where it is at a very close range zero.
2/10 of 1 thou to the left of a 200 m dead wind zero.
i call 1/10 of 1 thou 1 point to differentiate between that and 1 moa, in case sight radius causes 1 point to differ from a moa..
my self i prefer to have the staff verticle and put the spindrift on the windage foresight because it is easier for a lay person.
if using a fixed foresight, i would drift it in the dovetail to achieve a dead wind zero for 900 yd in a long range only rifle, as this is an average of 800, 900, and 1000.
going on the foresight rings you have made me over the years, you are far more qualified to establish the staff angle than i
i have in my possesion a raton wind flag to compare with our wind flags here in oz, and its angle of lift etc is very similar to ours.
getting back to establishing a dead wind zero, it sounds simpler than it is.
i now do it at 50 yds if possible, as there is less wind effect on the bullet there.
then adjust the sight to allow for spindrift before going to long range.
i do remember dan theodore explaining how he used spirit levels to allow for cant of the staff.
maybe someone has his writing about this stored somewhere?
bruce.

correction with apologies.
approx 1 moa is NOT as i stated 1/10 of 1 thou on the sight of correct radius.
it is 10 thou.
old age is a wonderful thing - sometimes
bruce.