9 O'clock vs 3 O'clock

[Texas Solo]

In this diagram, it shows a low POI from a 9 O'clock wind, but a high POI from a 3 O'clock wind. Why?

 

[geo.ulrich]

right hand barrel twist effect on bullet

 

[Rank Amateur]

See Magnus effect.

 

[Redd]

^^^^^^ what he said!^^^^^

 

[ELR LVR]

right hand barrel twist effect on bullet

Agreed, Twist rotation. Like a golf ball. Same principle.
Now if you go left hand twist, which is an option but I don't know why anybody would since a right hand twist only aids to keep the barrel tight in the action....then reverse the clock .

 

[G7BC]

In this diagram, it shows a low POI from a 9 O'clock wind, but a high POI from a 3 O'clock wind. Why?

Aerodynamic jump. Right to left wind pushes the bullet up, left to right wind pushes it down. In switchy conditions it will cause some vertical on target , if you're not compensating for it.

 

[Texas Solo]

I get spin drift, but thought a RH twist made it go right?

 

[G7BC]

I get spin drift, but thought a RH twist made it go right?

Yes, that's spin drift. But the vertical movement that your chart is showing you is Aerodynamic Jump. Kinda think of it like the bullet is a paddle wheel spinning clockwise, it will grab a right wind and pull itself up , or grab a left wind and pull itself down.

 

[boltfluter]

In my benchrest days we would say "right will rise and "left will lower". If you can't remember that, find another hobby! Lol.

 

[FeMan]

Aero dynamic jump is about a 1/4 minute per 5 mph of lateral wind. The actual amount depends on twist rate and MV but that is a decent approximation. It happens at the muzzle. Unlike spin drift, which varies with distance, aero dynamic jump is the same regardless of target distance.

 

[CharlieNC]

Just like a boat propeller "torques" a boat to run at an angle as it spins in the water, which is just a thicker fluid than air.

 

[ELR LVR]

I get spin drift, but thought a RH twist made it go right?

Yes spin drift is also within the same principle, climbing the air so to speak.
Right hand twist = Right spin drift.
I get a decent amount due to my velocity and twist rate
0.2 Mils at 600
and
0.6 mils at 1000
---------------------------
Unless there is wind
Then its up in the air as to how much it will go (no pun intended LOL)

 

[JFrank]

9:00 or 3:00 has a predictable outcome, the switch from 11:00 to 1:00 will kill you if you miss it.
Jim

 

[64Rambler]

Yep, this hold up at the range I shoot at as well, but only for left and right winds. For head and tail winds, it isn't so straight forward. Our shooting positions on the course (200, 300, and 600 yards) are elevated berms and most of the time, both head and tail winds actually raise POI because of updrafts created by the face of the berms. Very difficult to read. The goal is to just find a common condition before pulling the trigger.