Rifle Scopes Reticle cant - how to measure

[Peter83]

Hi guys. i have a Vortex Viper PST gen2 5-25x50 with MRAD clicks.

I noticed, that if i clik 10mil on elevation, the reticle will also move about 1 click to the left. With that result, how do i calculate how many degrees the reticle is canted compared to erector travel? It is not noticeable at all to the eye when just looking throu the scope, so i guess i cant be much?

Peter

 

[AIAW]

It's either unleveled or there is something wrong with the internals if you can see it like that. You have to have it 100 percent level to track-test it though.

Were you attempting to track-test it and that's how you were able to notice the gradual horizontal movement? Just curious as to how you were able to determine the horizontal component.

 

[Peter83]

It's either unleveled or there is something wrong with the internals if you can see it like that. You have to have it 100 percent level to track-test it though.

Were you attempting to track-test it and that's how you were able to notice the gradual horizontal movement? Just curious as to how you were able to determine the horizontal component.

Hi AIAW What i did, was lining up the reticle perfectly with the edge of a horizontal line in a optical boresighter, just touching the edge ( like this bore sighter in the picture i found on google ). After that, i dialed 10mil, and could see that the reticle now did not touch the edge anymore, but had moved just a hair away from edge, about the equal of 1 clik. Hope it makes sense, english is not my main langue i did try this servereal times, and was very cautious to align the reticle to the edge perfectly.

 

[Gohring65]

I would use a plum bob and set myself up behind the rifle, where I have a consistent hold. In other words, where I shoulder the rifle every time I shoot it. Line up the scope with the plumb bob and confirm with a tall target test. After confirmation I would set a anti can’t level on the scope tube and not worry about rifle cant. It’s more important to me to have a comfortable consistent hold every time i get behind the rifle.
granted you’re not holding at a 20 degree cant. Minor cant won’t be distinguished between shooter error or wind.

 

[86alaskan]

AS the others stated, make damn sure you're level before shooting long. Hang a plumb line, level the rifle and level the reticle to the line. Then run your tall target test to confirm tracking and any cant that you may have missed. If you're off by much, you can see it with your eye. When you're level, your eye and "natural" level can pick up anything over like 3deg of tilt.

 

[Peter83]

I appriciate the replys But still, there must be some degree of cant in the reticle, compared to the erector travel when there is movement to the side ( about the equal of 1 clik sideways ) over 10mil of elevation dial, and i am curious how to measure the degrees of reticle cant, if it possible to tell with the info i got?

 

[spife7980]

Yes. You get the linear measurements of what you have observed and use a little trig.

 

[Gohring65]

I appriciate the replys But still, there must be some degree of cant in the reticle, compared to the erector travel when there is movement to the side ( about the equal of 1 clik sideways ) over 10mil of elevation dial, and i am curious how to measure the degrees of reticle cant, if it possible to tell with the info i got?

I would probably send it back and have Vortex check it.

 

[hseII]

I appriciate the replys But still, there must be some degree of cant in the reticle, compared to the erector travel when there is movement to the side ( about the equal of 1 clik sideways ) over 10mil of elevation dial, and i am curious how to measure the degrees of reticle cant, if it possible to tell with the info i got?

1. Remove your scope from the rings.
2. Position your rifle in a rest & level the action using a level.
3. Install your scope & level your scope. 4. Now hang a plumb bob & verify your scope is plumb to the plumb bob string.

 

[Peter83]

Yes. You get the linear measurements of what you have observed and use a little trig.

Sry, i dont quite understand how to / what to do?

 

[Peter83]

1. Remove your scope from the rings.
2. Position your rifle in a rest & level the action using a level.
3. Install your scope & level your scope. 4. Now hang a plumb bob & verify your scope is plumb to the plumb bob string.

Thank you for the sugestion, but the reticle would still be canted compared to erector travel. With the reticle and rifle plump, dialing 10mil of elevation would still move POA about 1 click to the side. And if possible, i would like to know how many degrees the reticle is canted compared to erector travel.

 

[86alaskan]

Therein lies the rub..... you should have no horizontal movement when properly leveled. After 10mil of up only having .1mil is not that bad, but it shouldn't be there at all. So, either there is a problem with the scope, the mounting, or the ability to maintain true level while dialing.

 

[Peter83]

Therein lies the rub..... you should have no horizontal movement when properly leveled. After 10mil of up only having .1mil is not that bad, but it shouldn't be there at all. So, either there is a problem with the scope, the mounting, or the ability to maintain true level while dialing.

I agree But how do i translate the result to how many degrees the reticle is canted compared to erector travel? I know i can set the scope and rifle up so everything is plump, but that dosent matter if the reticle is canted compared to erector travel, and it would be nice to know the amount of cant in degrees i think

 

[86alaskan]

I suppose it would be a little trigonometry, find the distance traveled up, and the distance traveled over, then you can A2xB2=C2 to find the length of the longest side, then you can find the angle at the bottom of the triangle.

I will say, though, this is kinda like having a bad alignment on your car and compensating by steering to the left. there's problem that you know about and needs to be corrected, but you're just fighting your way around it.

 

[spife7980]

Sry, i dont quite understand how to / what to do?

You need to measure how much you dialed up and you need to measure how much it moved over.

So the amount dialed up is the side adjacent to the angle we are after, the amount it moved over horizontally instead of perfectly vertical is side opposite of the angle. With those two known measurements you can figure out the angle via the tangent function.

If youre set up at 100 yards lets say you dialed the 10 mils, at 100 yards that would equate to 36 inches. If it moved over .1 mils in that distance then thats .36 inches .

tan( θ ) = (.36/36)
θ = tan^-1 (.36/36)
θ = .5729°



Now... are you really sure that it moved .1 mils over or is it possible that you made a mistake or that the equipment shifted a tad? Because Im more inclined to blame the operator over a .1 shift than the scope. And even still, half a degree is nothing.

 

[b6graham]

what is the scope mounted to when you do then? you and a bipod? or secured to a confirmed level scope mounting/tracking test tool?

 

[hseII]

Thank you for the sugestion, but the reticle would still be canted compared to erector travel. With the reticle and rifle plump, dialing 10mil of elevation would still move POA about 1 click to the side. And if possible, i would like to know how many degrees the reticle is canted compared to erector travel.

It should not be canted.

Plumb is Plumb.

Either there is
1. operator error,
2. the scope is not perfectly perpendicular to the top of the rifle, or
3. there is an internal issue with adjustments, which is possible, but not as probable as #1 or #2.

I intend to purchase the scope you are referencing: please share your updates.

 

[Peter83]

Now... are you really sure that it moved .1 mils over or is it possible that you made a mistake or that the equipment shifted a tad? Because Im more inclined to blame the operator over a .1 shift than the scope. And even still, half a degree is nothing.

Thank you so much for the time to explain. Yes, i am very sure it moves .1 horizontaly when dialing 10mils of elevation. I tried it many times, and just tryed it again. With my math skills combined with my not native english langue, i am just not able to do the math you explained. But are you saying, that based on the info i gave ( .1 shift to the side when dialing 10mil elevation ) that would only mean a half degree of reticle cant compared to erector travel?

 

[Trigger Monkey]

The reticle is attached to the erector, they move together, so if you are seeing the reticle step out during it's travel, it's not reticle cant. Potentially, the issue could be the windage stalk that contacts the erector is not perfectly flat, it happens, and as the erector moves along it as you dial elevation, it manifests itself in the reticle stepping out.

The drawing is crude but gives a glimpse into the inner workings of an optic as you dial elevation.

 

[gnochi]

If your rifle is held perfectly steady and you dial 10mrad elevation, which happens?

1. Does your reticle end up at 10 Elevation 0.1 Windage, as viewed through the reticle at 0E0W
2. Does your reticle end up at 10E0W, as viewed through the reticle at 0E0W

In the first case, the turrets and reticle are canted to each other, which is bad. In the second case, the scope is canted to the rifle, which is an easy fix.

Either case can result in windage being a click off as far as the rifle is concerned.

Alternatively to having a perfectly steady rifle:

1. At 0E0W, shoot a group when aiming at a recognizable point
2. Dial 10mrad
3. Shoot a group when aiming at the same recognizable point
4. Aim the rifle at the center of the second group
5. Is the first group in line with the reticle or off to the side?

 

[JGottschall]

Thank you so much for the time to explain. Yes, i am very sure it moves .1 horizontaly when dialing 10mils of elevation. I tried it many times, and just tryed it again. With my math skills combined with my not native english langue, i am just not able to do the math you explained. But are you saying, that based on the info i gave ( .1 shift to the side when dialing 10mil elevation ) that would only mean a half degree of reticle cant compared to erector travel?

angle b would be .5729 Jeff

 

[spife7980]

Thank you so much for the time to explain. Yes, i am very sure it moves .1 horizontaly when dialing 10mils of elevation. I tried it many times, and just tryed it again. With my math skills combined with my not native english langue, i am just not able to do the math you explained. But are you saying, that based on the info i gave ( .1 shift to the side when dialing 10mil elevation ) that would only mean a half degree of reticle cant compared to erector travel?

Yeah, that math says only half a degree off with those numbers. Not enough to worry about and if you send it in for repair they will just say that its within their specs tolerance. Slightly canted that small amount is nothing.

BUT we dont necessarily know if thats what you are seeing. The bigger issue is what these guys above are talking about.

Is it actually the reticle thats canted?
If the reticle is canted in its relationship to the erector then it would still track properly... its just that if you set the rotated reticle up plumb then that proper tracking is pushing it off to the side an equal but opposite amount. In this situation at half the distance of travel (5 mils) it would only be half the amount (.05 mils), half the total you saw at the full 10 mils of travel, it would have a proper linear relationship thats just a bit skewed because of how you mounted it.

Or is it your erector thats to blame and is shifting over? The reticle could be perfect as far as its rotation goes but if the erector is shifting to the side thats an entirely different thing. It could make that shift anywhere in its range of travel, doesnt have to be equal and proportionate. .

You really should be mounting these ina fixture that removes all outside influence if youre trying to diagnose these issues.

 

[10ring'r]

1. Remove your scope from the rings.
2. Position your rifle in a rest & level the action using a level.
3. Install your scope & level your scope. 4. Now hang a plumb bob & verify your scope is plumb to the plumb bob string.

I am far from a "pro" and will not claim to be one, but the above procedure is what I would do, if I wanted to even come close to an educated guess, that my reticle was canted. I don't care how steady you are, you WILL NOT, be able to hold a rifle that perfectly still, I don't care how strong or how much muscle control you have. You have to eliminate the human factor from the equation. If you can see/observe the reticle moving that minute amount, it's moving at least 2x as much, send it back. Companies use specialized equip. to test scopes. Just my 2c worth. Mac

 

[Peter83]

Thanks alot for the replys guys! I dont know what is causing the slight shift in POA horizontaly, but it is repeatable, and dosent semm to happen all of a sudden, but more gratually as i dial the elevation. Althou the boresighter is no way near the proff stuff scope manufactors have, i actually think the result is legit since it is repeatable, and since every time i tryed, i made sure the reticle alligned perfectly with the edge of the vertical line in the sight picture. The result is consistant. Anyways, i wont worry about it, i guess i just gonna live with it. I thank you all for your input, i really appriciate it

 

[b6graham]

you're really failing to address most of what people in this thread are saying regarding mounting and scope tracking tests

 

[Ratch_V]

It may be possible you are maxing out your scope. The Vortex Viper PST gen2 5-25x50 says it has 10 MIL of windage and 20 MIL of elevation. Adjusting 10 MIL may be getting close to maxing it out. If you're near the limit one way or another, that would cause it to not track properly.

 

[Peter83]

you're really failing to address most of what people in this thread are saying regarding mounting and scope tracking tests

Sry, i thourgt i it told in the first post. The scope is mounted in a Spuhr SP 3602 on the rifle. The boresighter goes in the end of the barrel, so there is not really a problem with anything not stable sine the optical boresigter is attached to the end of the barrel, meaning that if the rifle moves, the boresighter/sightpicture moves with it. The rifle it self is sitting in two V shaped holder with rubber coatings.

 

[Peter83]

It may be possible you are maxing out your scope. The Vortex Viper PST gen2 5-25x50 says it has 10 MIL of windage and 20 MIL of elevation. Adjusting 10 MIL may be getting close to maxing it out. If you're near the limit one way or another, that would cause it to not track properly.

Yeah could be, but i made sure it was in the center of the travel range ( cant remember the english name for it ). I did the whole thing with counting clicks over the whole dial range, then clicking half those click so i landed in the middle og the adjusment range.

 

[b6graham]

i would recommend going out. zeroing the scope. at 100y/m

shoot a group at 100

dial 10 mils up. shoot another group. make sure you have enough vertical.

Store - Box to Bench Precision

Snipers Hide 100 Yard Scope Tracking Target - MIL - MOA - For Milliradian and Minute of Angle Scopes - True Minute of Angle - Precision Shooting -

www.boxtobenchprecision.com

i would bet your scope is ever so slightly not vertical in the mount. or maybe the rail on the rifle is goofy

 

[Peter83]

i would recommend going out. zeroing the scope. at 100y/m

shoot a group at 100

dial 10 mils up. shoot another group. make sure you have enough vertical.

Store - Box to Bench Precision

Snipers Hide 100 Yard Scope Tracking Target - MIL - MOA - For Milliradian and Minute of Angle Scopes - True Minute of Angle - Precision Shooting -

www.boxtobenchprecision.com

i would bet your scope is ever so slightly not vertical in the mount. or maybe the rail on the rifle is goofy

Even if the scope is a little off in the mount, it should still be able to follow a straight line down when alligning the scope with a vertical line in the optical boresighter. I dont really care if the reticle is canted compared to the scope body, i only care if the reticle is "canted" compared to erector travel. Because if it can follow a straight vertical line down without drifting out to the sides, you just level the reticle to a plumbline with the rifle being level ( the flashlight method i mean), and the elevation dial will do what is supposed to regardless if the scope body is not level since i would know that the elevation turret only apply vertical movement to the reticle I dont really use any shooting when testing af scope, there is to many variables. Wind, ammo, me, group size etc etc. I thank you for the reply, and i know many will say the same ( doing tall target test and all ), i just dont trust it is as accurate as a mechanical testing.

 

[Steel+Killer]

Your scope is automatically accounting for spin drift....It’s a new feature built into the Gen 2 PSTs......?

 

[Lowlight]

Many scopes, especially lower end ones will have a curve at the top,

Vortex is one we have tested that tends to curve as you add in elevation

I think I might have an old video that shows this on YT

 

[Steel head]

You need to measure how much you dialed up and you need to measure how much it moved over.

View attachment 7196233
View attachment 7196231

So the amount dialed up is the side adjacent to the angle we are after, the amount it moved over horizontally instead of perfectly vertical is side opposite of the angle. With those two known measurements you can figure out the angle via the tangent function.

If youre set up at 100 yards lets say you dialed the 10 mils, at 100 yards that would equate to 36 inches. If it moved over .1 mils in that distance then thats .36 inches .

tan( θ ) = (.36/36)
θ = tan^-1 (.36/36)
θ = .5729°



Now... are you really sure that it moved .1 mils over or is it possible that you made a mistake or that the equipment shifted a tad? Because Im more inclined to blame the operator over a .1 shift than the scope. And even still, half a degree is nothing.

Professor Spife has spoken!

 

[spife7980]

Professor Spife has spoken!

(Im just hoping I remembered how to do the trig correctly)

 

[AIAW]

Hi AIAW What i did, was lining up the reticle perfectly with the edge of a horizontal line in a optical boresighter, just touching the edge ( like this bore sighter in the picture i found on google ). After that, i dialed 10mil, and could see that the reticle now did not touch the edge anymore, but had moved just a hair away from edge, about the equal of 1 clik. Hope it makes sense, english is not my main langue i did try this servereal times, and was very cautious to align the reticle to the edge perfectly.

The problem is really that even if you perfect the math, you can’t correct for it by simply rotating the tube in compensation. You have just shifted the issue to a different plane.

These misalignment issues come in two flavors unfortunately - a problem or not a problem. You can correct a mounting issue (level to gravity). You can resolve issues with base centering. You can’t fix issues internal to the optic reticle position that are fixed or erector induced.

Like others have covered, if you are 100 percent sure it’s level, have Vortex take a look at it. It’s very difficult (and flawed) to use a bore sighter to do this testing though, especially the magnetic ones that attach to the muzzle. I wouldn’t bet on that bore sighter being the most accurate in itself.

 

[Peter83]

Your scope is automatically accounting for spin drift....It’s a new feature built into the Gen 2 PSTs......?

Lol i actually thourgt about it, but it moves the POI the wrong way

 

[Steel+Killer]

My .02 if it’s only one click / .10 of a mil around 10 mils that’s around 1000yds or a little over for a 6.5CM which amounts to about 3.6” of error if it’s repeatable just dial it out, but I would do an actual tracking test (shooting it at 100yds) and see what it’s really doing.

 

[Peter83]

The problem is really that even if you perfect the math, you can’t correct for it by simply rotating the tube in compensation. You have just shifted the issue to a different plane.

These misalignment issues come in two flavors unfortunately - a problem or not a problem. You can correct a mounting issue (level to gravity). You can resolve issues with base centering. You can’t fix issues internal to the optic reticle position that are fixed or erector induced.

Like others have covered, if you are 100 percent sure it’s level, have Vortex take a look at it. It’s very difficult (and flawed) to use a bore sighter to do this testing though, especially the magnetic ones that attach to the muzzle. I wouldn’t bet on that bore sighter being the most accurate in itself.

Yeah i see what you mean. I also agree that the optical boresighteres is not like a proff collimator scope, but they are actually pretty accurrate for the use i descriped. As long as there is a vertical line, that you can line the reticle up with, and the thing aint moving, i cant see why it shouldent be able to tell if there is any drift in POA when dial the elevation the way i descriped. I tryed this test with serveral other scopes, and i havent seen the reticle drift this much before.

 

[Steel+Killer]

Lol i actually thourgt about it, but it moves the POI the wrong way

Now you just have to get a LH twist barrel and you will be GTO problem solved.....?

 

[Hellbender]

How do you know your bore sighter is level? I've never used one, so maybe it's a dumb question....

What if the scope is not EXACTLY over the bore centerline? Does the bore sighter account for this?