Validating Spin Drift

[DesertBoy]

Have been working with a .257 Weatherby with my 11 year old son for about a year and half now. Shooting the 135 Bergers @ 3150FPS, 1:7.5 right twist. Gun shoots fantastic, the last three sessions at 950-1000yds he has shot 4-6" groups consistently. The days we picked to shoot were super early AZ mornings with pretty much zero to 2 mph winds. At these ranges the groups are great, but they are all pretty consistent at about 1 MOA to the right, every time. Gun is dead on at 100, and the right hand groups start to show up at about 700yds. Scope is definitely level and so is the level indicator. I have compared 3 different ballistic calculators, and they are all the same with the spin drift correction. I am wondering if the bullet is simply just drifting more than the programs are calling for?

 

[xsn10s]

Maybe try factoring Coriolis.

 

[DesertBoy]

Shooting west it was only .1 MOA correction as far as windage

 

[xsn10s]

Shooting west it was only .1 MOA correction as far as windage

Are you shooting near hills or canyons?

 

[DesertBoy]

It's a gentle rolling gas line road. Not a tricky place for wind, that's why we shoot there alot. And when there is wind, the way the geography is, it is generally a consistent wind with almost no terrain features to worry about. And the session before these two we were actually at the Berger 1000 yard range at Ben Avery which is a very forgiving range as far as wind goes.

 

[Idaho Lefty]

Try shooting 200 yard Group's about, a 1/4 inch to 3/8", Left of Target Center @ 200 ( Work's Perfect for Me with, a 6.5 Creed and 130 gr, ELD-M's ).
I Use a 200 Yard Zero ( Slightly LEFT of, center ) and "Dial" Range from There.
I Haven't shot 1,000 yd's with It,.. BUT, it's Bang ON at, 850 yds with, this 130 gr. Load at, 2,850 fps.
I'd do, at least, 5 shots or, better Yet, 10 shot Group's @ 200 ( Left of Ctr ) and Keeping, the Barrel,.. Cool !
Re-Check Zero at,.. 1,000 yds

 

[Eagleman Long Range]

Have been working with a .257 Weatherby with my 11 year old son for about a year and half now. Shooting the 135 Bergers @ 3150FPS, 1:7.5 right twist. Gun shoots fantastic, the last three sessions at 950-1000yds he has shot 4-6" groups consistently. The days we picked to shoot were super early AZ mornings with pretty much zero to 2 mph winds. At these ranges the groups are great, but they are all pretty consistent at about 1 MOA to the right, every time. Gun is dead on at 100, and the right hand groups start to show up at about 700yds. Scope is definitely level and so is the level indicator. I have compared 3 different ballistic calculators, and they are all the same with the spin drift correction. I am wondering if the bullet is simply just drifting more than the programs are calling for?

Eagle ballistics gives you a breakdown and corrects for everything

 

[std7mag]

I have a question!

What power range is your scope?
As in does it have enough power to see mirage?
I usually can't see mirage until about 20 power.

If you have a gentle mirage going from left to right, it will exastrabate the right hand drift.

My first 600 yard match I had a mirage going from left to right.
Wind flags set up higher were going from right to left.
I started chasing the wind flags, not realizing that they were higher than the bullet path.
Started shooting way right!
When I started correcting for the mirage instead, things came back in.

 

[DesertBoy]

I have a question!

What power range is your scope?
As in does it have enough power to see mirage?
I usually can't see mirage until about 20 power.

If you have a gentle mirage going from left to right, it will exastrabate the right hand drift.

My first 600 yard match I had a mirage going from left to right.
Wind flags set up higher were going from right to left.
I started chasing the wind flags, not realizing that they were higher than the bullet path.
Started shooting way right!
When I started correcting for the mirage instead, things came back in.

I have the NX8 4-32, and at that range my son likes it at about 26 power or so. We are generally out of there early enough before the mirage sets in. Going to shoot this coming Tuesday and we will see how it goes.