Spin drift seems excessive

[STOMP442]

I have built a 6mmBR for the wife on a Savage 11 action with a 26" Mcgowen 8 twist varmint contour barrel. The action is bedded in a Bobby Hart Bench Rest stock. She is running 105gr Berger hunting VLDs pushed by 29.0gr of H4895 in Norma cases and CCI small rifle primers at 2855 fps. Accuracy is excellent holding high .2's low 3's for five shots at 100 and 2-3" groups at 600. She uses this to compete in our local Prairie dog matches and she does very well even shooting perfect 10 for 10 scores on more than one occasion. She is a better shooter than me for sure. The problem we are having is there seems to be excessive spin drift beyond 200 meters. She can be zeroed at 200 and on a calm day she will impact about 2" right at 300 meters 4" right at 400 meters and 6" at 500 meters. I understand there may be wind components we may not be reading at various ranges but it is consistently running to the right beyond 200 meters on any given day. If she has a 5mph left wind she can hold center target and hit every target no problems. I am trying to figure out what the problem could be and any help would be appreciated. I am thinking of trying a different bulllet but I really do not want to give up the BC the Berger provides.

The scope she is running is a Leupold VXIII 6.5-20x50 mounted in lapped Talley rings. I have run the tall box test and checked for scope cant and the scope seems to track and function fine. I just don't know why this rifle wants to run to the right and spin drift seems to be the only logical explanation I can come up with but it seems excessive. Any help would be appreciated.

 

[savagedasher]

I have built a 6mmBR for the wife on a Savage 11 action with a 26" Mcgowen 8 twist varmint contour barrel. The action is bedded in a Bobby Hart Bench Rest stock. She is running 105gr Berger hunting VLDs pushed by 29.0gr of H4895 in Norma cases and CCI small rifle primers at 2855 fps. Accuracy is excellent holding high .2's low 3's for five shots at 100 and 2-3" groups at 600. She uses this to compete in our local Prairie dog matches and she does very well even shooting perfect 10 for 10 scores on more than one occasion. She is a better shooter than me for sure. The problem we are having is there seems to be excessive spin drift beyond 200 meters. She can be zeroed at 200 and on a calm day she will impact about 2" right at 300 meters 4" right at 400 meters and 6" at 500 meters. I understand there may be wind components we may not be reading at various ranges but it is consistently running to the right beyond 200 meters on any given day. If she has a 5mph left wind she can hold center target and hit every target no problems. I am trying to figure out what the problem could be and any help would be appreciated. I am thinking of trying a different bulllet but I really do not want to give up the BC the Berger provides.

The scope she is running is a Leupold VXIII 6.5-20x50 mounted in lapped Talley rings. I have run the tall box test and checked for scope cant and the scope seems to track and function fine. I just don't know why this rifle wants to run to the right and spin drift seems to be the only logical explanation I can come up with but it seems excessive. Any help would be appreciated.

I don't think it is spin drift . Sounds more like barrel timing . Larry

 

[jghoghunter]

I don't think it is spin drift . Sounds more like barrel timing . Larry

Someone is going to have to explain "barrel timing"

 

[XBBR Shooter]

It is cant, and it is common problem. It is not timing, and 200 to 400 yds/mtrs is too close to see measurable "spin drift".

Level the rifle and plumb the crosshairs.

 

[Rem06]

It is cant, and it is common problem. It is not timing, and 200 to 400 yds/mtrs is too close to see measurable "spin drift".

Level the rifle and plumb the crosshairs.

View attachment 983298

and then check scope vertical tracking, hang a plumb line at 100yds (thumbtack and weight or level) draw vertical line and spin turret 1 rev then 2 rev (or whatever MOA you like)and make sure group stays on line.

 

[tmwinds]

It is cant, and it is common problem. It is not timing, and 200 to 400 yds/mtrs is too close to see measurable "spin drift".

Level the rifle and plumb the crosshairs.

View attachment 983298

I think XBBR Shooter nailed it. Hang a string and plumb bob. Center your dot or crosshairs on the string. Run the elevation up and down. If you don't track up and down the string you either have a cant problem or a scope problem that is inducing windage when you change the elevation.

 

[6MMsteve]

Barrel Timing

 

[6MMsteve]

Yep Barrel Timing

 

[Ggmac]

Cant , or you can just adjust the barrels distributor a few degrees to make up for the improper barrel timing . Just kidding , I'm betting it's cant and again it's too close to test for spin drift at 400

 

[savagedasher]

Someone is going to have to explain "barrel timing"

The barrel bore isn't straight . The timing of the barrel is clocked or timed where the curve is going right from where the aim point is. Larry

 

[jghoghunter]

The barrel bore isn't straight . The timing of the barrel is clocked or timed where the curve is going right from where the aim point is. Larry

Thank you

 

[Ggmac]

Very possible , not probable , it should of been picked up if chambered and indexed with rods .

 

[savagedasher]

Very possible , it should of been picked up if chambered and indexed with rods .

Unless it has a custom chamber probably not . Really just adjust the scope and don't worry .. Larry

 

[Ggmac]

Could also have the scope not centered over the bore . A small bias will give the same results as CANT . Granted they are the same thing , sort of , but the scope mount ,ring set up can and is a problem with certain tolerance stacking . Think of a offset scope on a m-1 garand , it'll be adjusted for 100 and go further right at extended range , 200 , 300 etc .

Pm for ways to check

 

[savagedasher]

Looks like to me it has already ben checked .
But you must accept the barrel bore is crooked . A vertical line shooting it a 50 to 400 yard is a easy check . Larry

 

[Ggmac]

Not at all ! Most commercial actions , ah never mind . If the op want to check it , he'll pm me . Not getting into a useless talk with you .

 

[STOMP442]

Scope has been checked and rechecked. I installed it using the level level level. Rifle and scope are as leveled as i can get it. I have done the string and plumb bob test to eliminate cant and the scope tracks vertically just fine. If the barrel timing is the issue how does one time a pre fit savage barrel and still keep proper head space?

 

[XBBR Shooter]

Scope has been checked and rechecked. I installed it using the level level level. Rifle and scope are as leveled as i can get it. I have done the string and plumb bob test to eliminate cant and the scope tracks vertically just fine. If the barrel timing is the issue how does one time a pre fit savage barrel and still keep proper head space?

"Barrel timing" (whatever that is??) cannot cause this problem - IF you launch a bullet and it hits the POA at 100 yds, then it started it's life in a straight line - nothing in the barrel can cause it to start traveling in a different direction.

 

[DCRYDER]

I think that spin drift should push the bullet to the left unless you have a LH twist barrel.

 

[DCRYDER]

Are you aiming there is no wind or actually shooting over wind flags?