Canted Scope vs Canted Rifle

[TX_Diver]

Had the opportunity to shoot out to 1000 a few weeks back and found that as I got farther out I was needing to dial in additional windage (despite the wind being very light and no value into our faces).

Background:

I ended up having to dial 1.6 Mils left at 1000 yards.

I do not have a bubble level on my scope.

On the shooting line I leveled the crosshairs to the targets (by adjusting my bipod) visually based on the horizontal crossbeams that the targets hung from. It's definitely possible that they were still slightly out of level though. There is no guarantee that the target stands were perfectly level also.

From this is there enough info to determine where the issue is?

i.e. Assuming that the reticle is level to the bore of the rifle, but the rifle is canted due to my bipod, would I see the same need to dial in more and more windage as I get farther out?

Or is it more likely that my reticle is not level/plumb with the bore of the rifle (or my shooting natural shooting position).

All shots were prone off a wooden deck.

Please let me know if there is more info that would be helpful. Just trying to trace this back and see if I need to adjust how my scope is mounted.

Thanks!

 

[rduckwor]

Shoot a tall target test as described by Bryan Litz at appliedballistics.com. That will help determine your tracking accuracy. As for a canted scope, you definitely need to have the scope vertical in line with the barrel axis; use a level on the rifle and the scope for an easy fix. Adjust the scope until that level is where you want it. Careful tightening the rings as they may shift the scope level. Trial and error is the only way. As for canting the rifle, get a level, Amazon sells them for little $$. You don't have to spend megabucks for a level.

Good Luck,

RMD

<EDIT> Well, lookie here!: http://bulletin.accurateshooter.com/>

 

[Gunfighter14e2]

A canted erector is worst case.

 

[Sheldon N]

Only thing that matters in any significant fashion is whether the SCOPE was level to gravity. Canted rifle underneath has minimal effect, maybe a few inches at 1000 yards.

Level the reticle to a plumb line and put a level on your scope. Then check that the erector travel matches the reticle by shooting a tall target test.

My first guess with why you had to hold 1.6 mils is that the wind was doing something you weren't picking up. Second guess is that the target frame was not level and you were canting the scope to it. Finally don't forget that you're likely picking up a couple tenths of adjustment due to spin/coriolis at 1000 yards.

 

[TX_Diver]

I suspect I wasn't level to gravity as other people weren't having to hold or dial for elevation. Obviously we weren't shooting at the exact same time so there may have been some differences.

I will try to head out again after my vacation and see if I get the same results or something different.

Thanks all!

 

[2ndamendfan]

[No message]

 

[Belliger]

In Bryan Litz's Accuracy and Precision book he did a model of a 3 degree cant error (chosen because that is all the average person can resolve without a level). He modeled a 24.7" error at 1000 yards using a .308.

The targets at my range are anything but level being in movable stands. It makes me question everything looking at a angled target through my scope while my bubble reads level.

Like Sheldon said, it is not super important to have the scope level to the rifle. Many shooters who don't have a cant adjustable butt plate will cant the entire rifle and adjust the scope accordingly. So their vertical axis may be .5 inches off the bore axis. There will be some error, but at range it will be swallowed up by the inherit precision of the system.

The important thing is to have a bubble level on the scope to ensure that the scope is level to gravity.

Lastly the tall target test is a really good idea. It is possible that like Gunfighter said you have a canted erector. This could be caused by bad rings, improperly aligned rings (they are trying to twist the scope) or over tightened rings. Reuben at Vortex mentioned to me years ago that many of the tracking issues people called in about with the Razor Gen 1 were fixed by uninstalling and reinstalling the rings with less torque.