Question about misalignment of bore to scope

[LVLAaron]

Help me settle a debate.

Pretend your barrel is not perfectly aligned with your scope. Pretend the barrel points to the left a bit.

In the drawing, solid line straight ahead of the shooter/where your scope base is pointing. Dotted line is where the barrel is pointing.

You zero your rifle for 100 yards.

Assume spin drift and other factors dont exist. Because of the Scope/bore misalignment, does your point of impact continually move further away from your point of aim as distance increases? Or does adjusting your scope windage at 100 yards carry over to the further distances as well?

 

[PhilKeil]

I actually had a issue like this this past summer with a 300 BO AR we built for hog hunting..
In our situation it could be sighted in at 50 yd distance then move to 100 and it was way off. Then sight back in at 100 and way off at 50.
I could see a tweak to 1 side in the 1 piece mount from Vortex. It was not in a straight inline with barrel. I verified by placing the scope in a set of rings and it was ok at both distances. In placing in the rings I also found the scope would not track. I may have been because the mount was not straight. Sent mount and scope back and Vortex made it good. it works as expected.
Also in my pistol shooting I had a cmore red dot mounted on a carver mount on a Glock 17 L. A carver mount mount is well above the barrel and slide. You could only be sighted in for 1 distance. Anything other than that it was either high or low and depending on distance sometime by a large amount.
It came off i hated it.
Hope this answers your question
phil

 

[rwj]

Based on the diagram where I’m assuming the scope’s reticle is shown being located on the barrel centerline at zero distance, I’m thinking that the windage adjustment essentially changes your line of sight thru the scope so that once ”zeroed”, additional adjustments at different distances would not be required.

However, if the reticle was significantly laterally offset from the barrel centerline at distance zero, the above would not be true and windage adjustments would become distance dependent.

Heres to hoping an optical expert contributes to this thread!

 

[243winxb]

Off axis- impact continually moves further away from your point of aim.

The old Win M94 top ejection rifle with a side mounted scope is a perfect example of off axis.

 

[Ackman]

Help me settle a debate.

Pretend your barrel is not perfectly aligned with your scope. Pretend the barrel points to the left a bit.

In the drawing, solid line straight ahead of the shooter/where your scope base is pointing. Dotted line is where the barrel is pointing.

You zero your rifle for 100 yards.

Assume spin drift and other factors dont exist. Because of the Scope/bore misalignment, does your point of impact continually move further away from your point of aim as distance increases? Or does adjusting your scope windage at 100 yards carry over to the further distances as well?




View attachment 1223944

Is this just hypothetical, or and actual situation? I've experienced misalignment like that and it's not right. First check the scope mount alignment. A straightedge on either side of the mount(s) will show if it's the mount(s) not in line with the barrel. Then with the barreled action out of the stock, carefully put those straightedges along each side of the action. This will show if the barrel is off....it happens. If the barrel is true in the action, put a 1" tube about 3' long (from just about any hardware store) into the rings. See how far off the tube is from being centered wirh the muzzle. Easily corrected with Burris Signature ring inserts.

To answer your question....correcting windage at 100 will carry over to longer ranges, why wouldn't it.

 

[El Matador]

There will always be some misalignment between your scope body and rifle barrel. Windage adjustment will fix it at all distances, provided the scope is sitting directly on top of the bore axis. If the scope is offset laterally from the rifle barrel you will have some error present that will be magnified as distance increases, but it will usually be a very small amount. Take for example a scope that sits 1" to the left of the bore axis: With a 100 yard zero the bullet must move 1" to the left in order to intersect your line of sight. It will keep moving left at a rate of 1" per 100 yards until it hits something. Most scopes are going to be offset far less than 1" however, so it likely won't make any appreciable difference at practical shooting distances. The same concept holds true for a scope that's canted or tilted with respect to the rifle.

 

[PigButtons]

If it is truly a case of scope/rings/rail that is not aligned with the bore axis then if is is zeroed at 50 and x to the left at 100 it will be 2x at 150 and 3x at 200. Burris Signature rings, as Ackman said, are made with inserts to correct this exact type of problem, as well as to add elevation for long distance shooting. There are other rings that do the windage part pretty well with a set screw on either side of the rail clamps.

 

[gdbleb]

Have that very issue with one particular gas gun. March scope in a NF Unimount so presumably the quality is there. Move the whole assembly to any other rifle and it's back to the factory zero windage setting. No idea whether its the barrel or the upper rail. It hits the X ring at multiple distances so I don't mess with it. It DOES mess with my OCD though. Curious, what's the counter-argument?

 

[243winxb]

*Question- if the scope windage knob is turned till there is only a few clicks remaining, is this an Optical Off Axis condition?
I think yes, but not sure. Your thoughts?

Bushnell-
"CENTERING THE RETICLE
The reticle was carefully set at the optical center of your riflescope at our factory. This setting
provides you with the ideal adjustment range from the center position. The riflescope’s adjustments
are used to zero-in the riflescope.
It is wise to check the center of the optical axis before mounting. Do this by placing the scope in a
solid V-block (cardboard box with two slots). While looking through the scope in a normal viewing
position, carefully rotate the scope. If the target moves in a circle larger than 1” from center (at 25
yards) in relation to intersection of crosshairs, reset windage and elevation adjustments. Remove
adjustment caps. Set each adjustment to midpoint and recheck for centering. If reticle still rotates,
use adjustments to correct."

This is so we dont run out of adjustment, when sighting in.

 

[Ned Ludd]

A misaligned scope [horizontal] with respect to the bore axis would cause a deviant [horizontal] but straight trajectory (as viewed from directly overhead) with respect to the line of sight, as shown by the dashed line in your image. The line would not curve even farther to the left with respect to distance, as it would do if it were caused by wind deflection. In other words, if you were to calculate the leftward deviation of your dashed line from the line of sight at each marked distance (100, 500, 800 yd), you would find that it was constant in terms of angular displacement (MOA or mrad) at the various distances. So in theory, a single windage adjustment would correct the misalignment at the different distances. In practice, you might find that you had to play around with a bit to arrive at the best compromise for all distances, but you ought to be able to get it close. The problem in this scenario is that it's difficult to be 100% certain the scope misalignment is solely and purely horizontal (i.e. in the same horizontal plane) with respect to the bore axis, which could render finding a single windage adjustment that would perfectly correct the misalignment at all distances. If you have a canted scope base, the misalignment will almost certainly not be 100% in the same plane.

 

[KY_Windage]

Help me settle a debate.

Pretend your barrel is not perfectly aligned with your scope. Pretend the barrel points to the left a bit.

In the drawing, solid line straight ahead of the shooter/where your scope base is pointing. Dotted line is where the barrel is pointing.

You zero your rifle for 100 yards.

What you are describing is the situation with almost every scope after it is mounted and before it is sighted in. There is almost always a windage correction needed, otherwise it is off at an angle, just like your drawing. And with an angle, the farther you go, the more you are off.

Make sure your reticle is pointing at the exact center of your bore, then make sure that when you shoot your reticle is level. Then no matter where you sight in (100 yds, 200 yds, etc.) you will not have windage errors at other distances (except those caused by the actual wind, of course). I posted how to do this in a thread of yours last August, I think it was. It is some work, but it is free and foolproof.