spin drift

[phorwath]

Originally Posted by mikebob

This thread is pretty darn good I must say. I was just wondering why couldnt a guy set up a target at 1000+ yards, wait a very long time here in OK for a windless day and zero windage at that range for dead center impact. Then shoot at 100 yards, the distance you are off would have to be spin drift wouldn't it. Then zero back at water ever range you zero at and add that distance as wind drift (break down into mph) like shawn. Would that work I now it wouldn't be perfect but it would close. I think it would be more off at closer range that at 1000 but then it would be easier to account for at closer range also. Heck I am tired just babbling somebody slap me if im getting off base into stupidness.

mike

That's precisely what I did also. I first zeroed dead on at 990 yds on windless days. Then I came back and shot at 300 yds and measure the leftward impact at 300. From there I could calculate the total left to right drift from 300 to 990 yds. Then I subtracted Coriolis drift from my total drift to determine spindrift. You could also shoot at 100 yds or 200 yds, and those might be better yardages. I used 300 yds because that's where I shoot to check my rifles zero prior to heading out hunting and I wanted to know the left dope required at that yardage to be dead on at 1000 yds.

[jwp475]

Originally Posted by Eaglet

Sorry, I did not see phorwath's last post.

Using LoadBase 2.0 I got the following results:

SF for 7mm = 1.52
SF for 300 = 1.79

Is that 1.52 & 1.79 inches at 1K?

[Jeff In TX]

Originally Posted by mikebob

This thread is pretty darn good I must say. I was just wondering why couldnt a guy set up a target at 1000+ yards, wait a very long time here in OK for a windless day and zero windage at that range for dead center impact. mike

Mike,

I'll make you an offer, then next time we get a totally windless day in here in Texas or OK let's get together and give this SD a whirl? Well, we'll probably never meet under those conditions, but if you ever venture down to TAC PRO here in Texas and want to shoot at a grand under tornado conditions (those are pretty much our calm days) let me know.

[mikebob]

Originally Posted by Jeff In TX

Mike,

I'll make you an offer, then next time we get a totally windless day in here in Texas or OK let's get together and give this SD a whirl? Well, we'll probably never meet under those conditions, but if you ever venture down to TAC PRO here in Texas and want to shoot at a grand under tornado conditions (those are pretty much our calm days) let me know.

Thanks for the invite,
i am in texas often on business I just might drop in if I am close to that area.

If your ever this way give me a shout I have some brand new targets I made without a bullet hole one in them yet.

[Eaglet]

Originally Posted by jwp475

Is that 1.52 & 1.79 inches at 1K?

That's the bullet SF = Stability Factor to plug into Michael's formula to calculate Spin Drift.

SD = (2SF)(Time of Flight)²