Scope Not Level With My Action

[DavidleeCole]

I fought this at first and now I just have a 25lb weight hanging from a 3/4" rope at 100yrds on my zero range. I just use bags and a bench get my stock in my shoulder the way I like it so it feels right in the field. Then I plumb the reticle and tall target test and box drill at 100 yards with 10 mills dialed vertical and horizontal. This is done on a target with plumb and level box and vertical horizontal lines drawn. What ever the difference I turn to Brian Litz cant and scope dial correction calculations and figure offset and true dial factors. But you can just test to see how true it is and just roll with it if that's your thing.

 

[John Klingenberg]

Those levels that go in the action are rarely on. I put a machinist level on my mount and coincide it with my scope. Its rately given me a problem.

 

[Josh P]

This and a plumb bob

 

[rcoody]

I like this little gadget. Never put much faith in a 2" bubble level. Getting the rifle level before levelling the scope is an issue too. This little gadget doesn't require that.

Now i always check with a plumb bob afterwards

https://arisakadefense.com/products/optic-leveler

 

[ducky]

Wondering if anyone has run into this. I mount my scope and use one of those small levels that fits in the action and then sit a bubble level on the turret of my NXS. I get it so the bubbles match perfect. After shooting it at distance I can tell it's canted.

Yes I've had your exact same problem, I figured out the problem pretty quickly as my vertical crosshair was in the 1 & 7 o'clock position. It was a stock issue as the action inlet wasn't quite level. So I knew I didn't have the proper tools too square everything up, so I dropped it off with my gunsmith. He confirmed what I thought to be the issue, and had it back to me tthe next week.

 

[Canhunter35]

Nightforce specifically says to not level off their turrets
I've never had any issue with levelling off other brands of turrets

 

[Gcan]

I'm not sure this is the place for this subject: not all right/left POI shift is scope related.
I actually built a very precise adj fixture for Setting plumb on a scope. I can dial neg or *** roll to seconds.

Barrel indexing must always be considered. You can have a scope dialed in exactly 00.00.00 and still have right/left POI shift at distances. This is particularly true of Rems and other off the shelf OEM guns. Also true for many so called "Custom" guns built by ppl who think action/chamber alignment only. Every barrel bore has a bow in it. No bore is perfectly straight. Even with the barrel chambered and mated to the action perfectly, if the muzzle/bore variation is not indexed perfectly in the vertical alignment then a 100 yard windage zero can be off by MOAs at 1000 yards with a perfectly set up scope. In other words the scope is tracking 6 to 12 O'clock but the muzzle is pointed 7 to 2 O'clock. Your POI will be farther to the right the farther you shoot.

I use my jig to align the scope to where the gun prints. If I'm level but the gun shoots 1 moa right at 1000 I use my jig to move the scope to match the barrel.

Thought Id add:



Initially I set my rifle/scopes up with a level and a plumb bob. I zero the rifle for elevation and windage at 100 yards.


I then dial in my ups and shoot 1000. From that point I never look to the level again.


I set up Precision machine tools for years. Its hard enough to dial in a couple thousandths with a 12" Precision level. I do not believe anyone can use a 2" level on a rifle scope and get an adjustment of 2 moa. That would be 3/10ths of one thousandth of rotation or .0003".


My jig has a 3.000" arm. (3" Radius) from center axis of scope tube to the contact point for a .0001 indicator. The diameter of the theoretical circle is 6.000". 6" x 3.1416" = 18.85" circumference/360 degrees = .0523" rotation per 1-degree. / 60 minutes of angle per degree = .000872" of rotation per MOA.

At some point tangent/secant (whatever) has to be converted into a linear distance that can be measured.


Once set up and the indicator zeroed,

The rings are loosened slightly.


The jig uses a captured jacking screw clamped to the scope that jacks against an arm mounted to the base to rotate the scope.


My jig holds the scope tube in relationship to the base and then uses an independent jacking arm with an indicator. I simply dial in the "fix" and lock the rings. I release the jacking clamp. If my indicator still shows the same value I'm done.


Once a rifle is set up like this the scope/rings are set to that gun's barrel only and cannot be switched to other guns without re setting to the new gun.


There will be no photos. Sorry. Took me a long time to design and build this thing.


Once done, a rifle with a quality scope will track +/- 0 MOA right/left windage to infinity and back to 100.

 

[gilk1]

I'm not sure this is the place for this subject: not all right/left POI shift is scope related.
I actually built a very precise adj fixture for Setting plumb on a scope. I can dial neg or *** roll to seconds.

Barrel indexing must always be considered. You can have a scope dialed in exactly 00.00.00 and still have right/left POI shift at distances. This is particularly true of Rems and other off the shelf OEM guns. Also true for many so called "Custom" guns built by ppl who think action/chamber alignment only. Every barrel bore has a bow in it. No bore is perfectly straight. Even with the barrel chambered and mated to the action perfectly, if the muzzle/bore variation is not indexed perfectly in the vertical alignment then a 100 yard windage zero can be off by MOAs at 1000 yards with a perfectly set up scope. In other words the scope is tracking 6 to 12 O'clock but the muzzle is pointed 7 to 2 O'clock. Your POI will be farther to the right the farther you shoot.

I use my jig to align the scope to where the gun prints. If I'm level but the gun shoots 1 moa right at 1000 I use my jig to move the scope to match the barrel.

How do you correct this situation? This would require skewing the scope to match the bore curve, would it not? And how do you discern poi shift due to bore curve at that distance from spin or wind drift, parallax error, mirage, etc.? The error from 1deg of barrel curve at 1000yds from a rifle with a 26"barrel and 100yd zero is only 0.33moa (see attachment). That seems irrelevant and unmeasurable to me.

 

[RSRW]

I had this problem with a rather expensive Vortex scope. I contacted Vortex tech support and they told me that the top of the turret can indeed be off slightly (did not specify how much "off" is). They recommend using the plumb-bob method. I was also told to alternate the tightening of the ring screws to help eliminate roll. I tried it and it worked great.

 

[gilk1]

Thought Id add:



Initially I set my rifle/scopes up with a level and a plumb bob. I zero the rifle for elevation and windage at 100 yards.


I then dial in my ups and shoot 1000. From that point I never look to the level again.


I set up Precision machine tools for years. Its hard enough to dial in a couple thousandths with a 12" Precision level. I do not believe anyone can use a 2" level on a rifle scope and get an adjustment of 2 moa. That would be 3/10ths of one thousandth of rotation or .0003".


My jig has a 3.000" arm. (3" Radius) from center axis of scope tube to the contact point for a .0001 indicator. The diameter of the theoretical circle is 6.000". 6" x 3.1416" = 18.85" circumference/360 degrees = .0523" rotation per 1-degree. / 60 minutes of angle per degree = .000872" of rotation per MOA.

At some point tangent/secant (whatever) has to be converted into a linear distance that can be measured.


Once set up and the indicator zeroed,

The rings are loosened slightly.


The jig uses a captured jacking screw clamped to the scope that jacks against an arm mounted to the base to rotate the scope.


My jig holds the scope tube in relationship to the base and then uses an independent jacking arm with an indicator. I simply dial in the "fix" and lock the rings. I release the jacking clamp. If my indicator still shows the same value I'm done.


Once a rifle is set up like this the scope/rings are set to that gun's barrel only and cannot be switched to other guns without re setting to the new gun.


There will be no photos. Sorry. Took me a long time to design and build this thing.


Once done, a rifle with a quality scope will track +/- 0 MOA right/left windage to infinity and back to 100.

So you're rotating the scope to account for perceived barrel warp? Won't that affect your vertical poi? Of course it will. Unless I'm misunderstanding, and correct me if I am, you're correcting for an immeasurable and possibly nonexistent problem in one direction and introducing a definite/measurable error in another direction.

 

[David Lindler]

Wondering if anyone has run into this. I mount my scope and use one of those small levels that fits in the action and then sit a bubble level on the turret of my NXS. I get it so the bubbles match perfect. After shooting it at distance I can tell it's canted. I do a ladder test and confirm it's off.
So I get the gun set up and verify the action is perfectly level. I hang a plumb bob 80 yards away and sure enough its canted at about 11:57. With the bubble on the turret the bubble is touching the line while it's perfectly centered on the action. I checked both bubble levels on two quality levels I use for construction and both were on. I should've gone to the plumb bob to begin with. Is it unusual for a turret on a quality scope to not match the action.

Try lapping the scope rings. One may be a little off

 

[barrelnut50]

Scenario 1: Your scope is 10deg canted to the bore axis but is plumb. The horizontal poi shift due to that cant @1000YDS (expressed as x & h is scope height) is
x=htan(theta)=2.5"tan(10deg)=0.44"
And this is true at all ranges.

Your Scenario 1 analysis is not quite complete. Most folks will zero at 100-200 yds. For a 100 yd zero the .44" horizontal POI offset in your calculation creates a .44 IPHY angular POI error that is proportional to target range from 100 yds. At 1000 yds, for example, that angular error corresponds to a 4" POI shift. Not huge, but not zero either.

So, you want to pay attention to the reticle alignment with respect to the rifle bore. It doesn't have to be perfect, but it's worth getting the reticle alignment error down to 6 degrees or less. BTW, 6 degrees is equal to the angle between 12:00 and 12:01 on your analog wrist watch - it's not easy to gauge such small angles when looking at short distances.

 

[Alibiiv]

Great thread! Am fighting this very issue on my Savages.
Aligning the reticle with the plumb line on the wall and then using tape to hold it while tightening certainly would seem to make sense.
Can you elaborate on how you position the light to project the reticle? If the light is not aligned with the centerline of the scope, doesn't it project the reticle at an angle?
Thanks!

I align my scopes in the basement with a plumb line that is done with a wide, plumb magic marker line on my garage door. I use a Tipton gun vise/cradle that is on top of my work bench that is level so if I move the Tipton around some on the bench to line up the plumb line I don't lose level of the rifle. Depending on the rifle I will put my scope base/s and scope rings (bottom half) on the rifle. I then level the rifle off of the receiver, and...tape it in place on the Tipton vise so it cannot move. I then put the scope into the bottom rings, and then the top scope rings on and snug the top rings down until I can just move the scope with minimal effort. I move the center of the scope crosshairs until they are centered on my plumb line and then move the verticle crosshairs until they are parallel with the plumb line on the door, and then masking tape the scope to the stock. I always keep checking for the rifle being level throughout this process. I have checked this process with a 100 yard plumb line at the range at my club and have found the crosshairs to be plumb with the plumb line.

 

[gilk1]

Your Scenario 1 analysis is not quite complete. Most folks will zero at 100-200 yds. For a 100 yd zero the .44" horizontal POI offset in your calculation creates a .44 IPHY angular POI error that is proportional to target range from 100 yds. At 1000 yds, for example, that angular error corresponds to a 4" POI shift. Not huge, but not zero either.

So, you want to pay attention to the reticle alignment with respect to the rifle bore. It doesn't have to be perfect, but it's worth getting the reticle alignment error down to 6 degrees or less. BTW, 6 degrees is equal to the angle between 12:00 and 12:01 on your analog wrist watch - it's not easy to gauge such small angles when looking at short distances.

Incorrect, the horizontal poi shift is 0.44" at all ranges - it's not an angular error, it's fixed. The reticle is plumb so the turret adjustments are purely vertical and the bullet drop is vertical so they are parallel but offset 0.44", always.