Mounting an anti-cant bubble level

[Dave King]

This last Friday I got smarter, again!! (Many folks would say this is a daily event for me.. /ubbthreads/images/graemlins/smile.gif)

While I was leveling my rifle to mounting a new scope it came to me that I normally performed this task on a level surface...

Okay that's confusing so let's talk X, Y and Z axes. The X axis would be the one determining of the rifle is canted (corresponding to the horizontal reticle line in the scope) around the Z axis (a line running straight through the centerline of the scope (line-of-sight line)) and the Y axis would be a line corresponding to the vertical reticle line.

Back to the discovery...

When I mounted my anti-cant level I checked the rifle level on the X axis BUT FAILED to ensure the anti-cant level was perpendicular (90 degrees offset) to the Z axis. SOooo on Friday I mounted the new scope but immediately noticed that if I checked the rifle level (un-canted) on an inclined rifle target (changing the Z axis away from -0-) I WAS FORCED to induce cant to keep the installed bubble level indicating -| O |- level.

Soooo, now I'm on a quest to not only level the anti-cant devices on the X axis but to also ensure they're perpendicular to the Z axis. This should allow me to get an accurate X axis level indication for inclinded fire events.

voilà

 

[jb1000br]

Dave -- i just have a 20$ b-square level bolted on my 308 with no other thought than how tight to torque it. Didnt hurt me on the angled shots at ASC last weekend /ubbthreads/images/graemlins/wink.gif And if the angle doesn't get you there, it wont get you anywhere! /ubbthreads/images/graemlins/grin.gif

BTW -- you coming to the next one in may? 13/14 or 20/21 -- i'll try to get to the 13/14 match because the 20th will probably be a williamsport match...

Cheers,
JB

 

[Ian M]

Dave,
Very clear, concise explanation but you lost me after saying you were doing something last Friday /ubbthreads/images/graemlins/smirk.gif

You need to get a DeadEye Scope leveler - if you put the little arrow shaft deely out at 100 yards and center the two little wiggly bubbles in the glass tubes the crosshairs are up and down. That is my Gunsmithing 101 class for today /ubbthreads/images/graemlins/tongue.gif

 

[davewilson]

Dave,
maybe i'm missing something but it doesn't matter where the X is pointing,because it will always be perpendicular to the Z.what you're having trouble with is the gun is not moving on the true Y axis.

 

[rwleonard]

I think I understand what he is desribing. If, when you elevate or depress the muzzle, the level does not rotate around its longitudinal axis, you will induce cant in the level, which if you try to "correct" induces cant in the rifle.

Hey, maybe you could just mark on the level how much a 5 degree elevation shoves the bubble over and use it for an inclinometer too! No, that won't work. You wouldn't know what shoved the bubble out, cant or incline. You could use an inclinometer and the appropriate mark, though.

Rick

 

[Dave King]

Dave Wilson

You mention the "...it doesn't matter where the X is pointing,because it will always be perpendicular to the Z." but the problem is that the anti-cant level (X) can be mounted so that it's not perpendicular to scope centerline (Z). That's the problem as I see it, mis-matched or not perpendicular X and Z. The little B-Square levels and possible others of this type can be skewed a bit when mounting and they're so short that even a little skew make for a significant error.


R W Leonard

I believe you have the idea.

The scope level isn't on the 'true' X,Y,Z axis intersection with all angles perpendicular. It's probably better described as mounted on the plane of the X, Y and Z with the X and Y axes perpendicular but the X and Z axes NOT perpendicular. The angle of intersection of the centerline of the anticant level (X axis plane)isn't 90 degrees to the centerline of the rifle scope or rifle bore on the Z axis plane. As you describe, when the rifle muzzle is elevated or depressed the rifle must be canted to correct for the anti-cant level mounting error.



I believe I'm going to mill a device for my Picatinny rail that has a bubble on the Z axis and a bubble on the X. Also this device will be hard milled at a 90 degree intersection on the Z and X. In essence I'll have an anti-cant and inclinometer as you mention.

 

[davewilson]

Dave,
i got cha now.basically the Z of the leveling device and the Z of the scope are not parralel.i was only thinking of the scope.

 

[Dave King]

Dave Wilson

Yup!! That's it, mismatched/non-parallel Zs, I'm gonna get that problem fixed real soon.