Leveling a scope

[bigHUN]

Preliminary step to lapping, which is checking for concentricity and proper alignment. These FX no limits were good, so no lapping required

I was planning lapping my rings for the new Falcon long range scope, but only when I removed them from the old scope realized that my eaglevision adjustable rings rated "30mm" are slightly larger ID hole and having that black protection ring fabric so no touching metal on metal. I see that fabric is becoming popular lately.

The second thing also noticed (with a lazer pointer) that on my FX Impact the Picatinny rail if centered in the rifle body then it is off center from barrel centerline. Yes I know this is adjustable, I needed to offset littlebit to left (as much the screw heads allowing) for two centerlines be parallel as much possible. I don't like that machining error because co-linear/parallel @20 and @200 is not the same angle.

 

[nervoustrig]

FYI, if the scope rail is merely offset slightly to one side, that error will be erased as soon as you clock the reticle into alignment with the muzzle (rotate the scope body in the rings until the reticle lines up with the muzzle).

The 20yds vs. 200yds problem you describe only arises if the rail is angled off to the left or the right. By that I mean the rail is pointed laterally at a divergent angle relative to the bore.

 

[bigHUN]

FYI, if the scope rail is merely offset slightly to one side, that error will be erased as soon as you clock the reticle into alignment with the muzzle (rotate the scope body in the rings until the reticle lines up with the muzzle).

It is more then just that - pointing a lazer mounted at front of the rail to allign to a bore lazer at given distance let say 5 meters in my room or 30 meters in my backyard is not a same, but basically yes this is a way to minimize the error. My question to myself how much can I trust a chepo Chinese picatinny mount lazer pointer for $5 to do this job.

I am talking about centering a rail only with a bore as a #1 step.

I did not had a chance to enlarge/slot the rail screw counterbores but completely aligning the rail parallel to the bore shall be done exactly on top of the bore.

You are right about mirror method as a step #2

 

[GeneT]

I'm a little confused by some of what is in this thread. You can mount your scope at a 23.715* angle, and as long as you hold it there, reliably, every time, everything will be just fine. There is ZERO problem doing this. There is no such thing as 'directly over the bore' - you're talking about two tubes (barrel and scope) and the only thing that matters is that their axis align in a single plane, somewhere. All that matters is that when you hold the gun, the crosshairs are vertical and horizontal. That is all you are trying to do with scope leveling. If the crosshairs are not parallel and perpendicular, then your adjustments (elevation and windage) will have some error proportional to the cosine of the deviation from 'ideal'. That is it. You can mount a scope on an offset at 45*, or any other angle, you can mount your scope at any cant (with respect the the gun) that you want. All that matters. ALL that matters, is that the crosshairs are vertical and horizontal when you're holding on target.



GsT

 

[nervoustrig]

Agreed. Here’s how I like to put it:

1. Mount the scope so the vertical bar of the reticle is oriented to the bore (muzzle). This step eliminates scope cant. 
2. Then install a spirit level that shows level when the reticle is held level (vertical bar matches a plumb line). From that point forward, hold the gun level according to the bubble. This step eliminates gun cant.

 

[DML908]

I'm a little confused by some of what is in this thread. You can mount your scope at a 23.715* angle, and as long as you hold it there, reliably, every time, everything will be just fine. There is ZERO problem doing this. There is no such thing as 'directly over the bore' - you're talking about two tubes (barrel and scope) and the only thing that matters is that their axis align in a single plane, somewhere. All that matters is that when you hold the gun, the crosshairs are vertical and horizontal. That is all you are trying to do with scope leveling. If the crosshairs are not parallel and perpendicular, then your adjustments (elevation and windage) will have some error proportional to the cosine of the deviation from 'ideal'. That is it. You can mount a scope on an offset at 45*, or any other angle, you can mount your scope at any cant (with respect the the gun) that you want. All that matters. ALL that matters, is that the crosshairs are vertical and horizontal when you're holding on target.



GsT

Maybe I don't quite understand what you are saying, but if you cant your rifle, the projectiles will only hit the point of aim at one distance. The bore is no longer in line with the reticle. The higher the scope is mounted above the bore, the greater the error.

I have seen expert riflemen shoot with their rifle canted, but they only shoot a fixed distance. 

 

[lbc_PSI]

Agreed. Here’s how I like to put it:

1. Mount the scope so the vertical bar of the reticle is oriented to the bore (muzzle). This step eliminates scope cant. 
2. Then install a spirit level that shows level when the reticle is held level (vertical bar matches a plumb line). From that point forward, hold the gun level according to the bubble. This step eliminates gun cant.

Step 1 insures that the reticle is aligned with the bore. It does not necessarily eliminate scope cant. The scope and rifle system can still be canted.

Step 2 will only eliminate gun cant at all angles if the bubble motion is exactly 90 degrees to line of bore. If the bubble level is not perfectly machined, glued, and attached at the perfect 90 degrees to line of bore the bubble will only work at the angle at which the system was leveled. Point the system up or down and an imperfectly made or attached bubble level will have run-out causing the level to give an incorrect read.

 

[GeneT]

I'm a little confused by some of what is in this thread. You can mount your scope at a 23.715* angle, and as long as you hold it there, reliably, every time, everything will be just fine. There is ZERO problem doing this. There is no such thing as 'directly over the bore' - you're talking about two tubes (barrel and scope) and the only thing that matters is that their axis align in a single plane, somewhere. All that matters is that when you hold the gun, the crosshairs are vertical and horizontal. That is all you are trying to do with scope leveling. If the crosshairs are not parallel and perpendicular, then your adjustments (elevation and windage) will have some error proportional to the cosine of the deviation from 'ideal'. That is it. You can mount a scope on an offset at 45*, or any other angle, you can mount your scope at any cant (with respect the the gun) that you want. All that matters. ALL that matters, is that the crosshairs are vertical and horizontal when you're holding on target.



GsT

Maybe I don't quite understand what you are saying, but if you cant your rifle, the projectiles will only hit the point of aim at one distance. The bore is no longer in line with the reticle. The higher the scope is mounted above the bore, the greater the error.

I have seen expert riflemen shoot with their rifle canted, but they only shoot a fixed distance.

That assumes that the crosshairs are level with the rifle. You can cant the rifle however you want, and if the crosshairs are level when the rifle is canted everything behaves the same as when you hold the rifle 'level' and the crosshairs are level with the rifle. Scope height magnifies any angular error - which is to say, the degree to which your crosshairs are not level when you fire (regardless of how much or how little the rifle might be canted). For most people this error is inconsequential until you go to extreme ranges. I like a low scope only because it makes getting a close-range zero easier. 

 

[lbc_PSI]

I'm thinking about the airgun, scope, and bubble level in terms of a system consisting of axes similar to that in an archery sight. I won't bore you with the archery details, as there are plenty of youtube videos for that. ;-)


I see the system having 3 axes. Axis 1: Scope to line of bore. Axis 2: Reticle to line of bore. Axis 3: Bubble at 90 degrees to Scope/Line of Bore. Bubble at 90 degrees is not the same as the bubble bracket being at 90 degrees. The bubble can be misaligned in the bracket.
So here's the system parts. Yes, you have to use your imagination.

Ideally the scope will align with the bore and not be misaligned because of “bad rings”..

Once the scope is aligned to the bore (axis 1)..

..and the vertical reticle adjusted to intersect the bore (axis 2), then a bubble level can be mounted to the scope and adjusted to the reticle (axis 3). Assuming the bubble level is machined and assembled properly, when mounted, it will be perpendicular (90 degrees) to the line of bore.

When everything is properly aligned, titling the system up or down will not cause “bubble runout”.

When the bubble in the bubble assembly is not perpendicular to the scope and line of bore, it can appear to be level when the system is level.

If poorly aligned, assembled, or constructed, the bubble will “runout” left or right depending on whether the system is aimed uphill or downhill.

This condition, bubble axis inside the container/holder not 90 degrees to the line of bore, will cause the vertical reticle to cant when the shooter attempts to center the bubble.

High-end archery sights have a 3rd Axis micro-adjust so the vagaries of bubble level axis and machined axis and glued axis can be adjusted to a true 90 degrees. So no left or right impacts when shooting uphill or downhill.


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[Dingfelder]

Really well illustrated/explained, thanks!