Vortex Viper PST reticle cant

[Phelixx]

I have a Vortex Viper PST 4-16x50.

I recently got an ACD and through the process of mounting it it appears that my reticle is canted .2 degrees to the left in relation to the elevation turret cap. I found this by using 2 digital levels along the rifle receiver and the turret cap in conjunction with a plum bob at 50 yards.

So my question is:

How common is this degree of cant in lower end tactical scopes?

How much will it effect my shooting?

Vortex said they would replace my scope, but Im worried I will just get sent back another one with the same or worse cant if this is just what their tolerances are.

 

[bruce_ventura]

I'm impressed that you took the time to measure the alignment error. You must be as OCD as I am.

I'm confident that the manufacturing variation at the factory is larger than 0.2 deg. I regularly see errors larger than that magnitude in production scopes. You probably have a good sample. I would not exchange it.

The worse-case aiming error is only 1-2" at 1,000 yds, which isn't much by most standards. You can mitigate that error somewhat, depending on how you align the ACD to the scope. I recommend that you plumb the elevation turret axis if you're dialing elevation, or plumb the reticle if you're holding off elevation. There may still be a small aiming error, however, when dialing a large elevation and hold off a high crosswind correction. Even still, error in wind estimation will probably dominate the reticle cant error.

FYI, most spirit levels used in ACDs have a sensitivity of 0.25 deg per millimeter of bubble movement. In the field most people will have difficulty holding the rifle cant during a shot to better than +/-0.25 deg (+/- 1 mm of bubble movement). The alignment error in the scope reticle is already lower than typical cant errors when an ACD is used.

 

[Phelixx]

Hmmm.

Thank you for this reply. It actually makes me feel better about the issue. Maybe I wont return it. Vortex told me this morning that its a grey area for them so they would need to check it out and cant guarantee me anything over the phone.

 

[bigngreen]

If I remember right the spec that some other optics manufactures use is 3% out, don't know about vortex, heck just putting a level on the cap does not really tell you anything other than the reticle and cap have a .2 cant, I would check the reticle to turret movement.

 

[joeycoates]

I have a 6-24x50 PST in FFP that I just received Thursday and it has a little bit of cant as well. I checked it against a door jab at my house which I too used a digital level and verified that the door jab is vertical (89.9 degree's which is actually pretty good if you have ever tried to measure wall/jabs at your house, you would be amazed at how many are not vertical). Anyway, my reticle is also canted a little bit to the left. Unlike you I have not measured the exact amount as my level is simply too large to reliably put on top of the cap to measure the exact difference, but it is off by a small amount. Very small to be sure, but it is none the less off.

I first noticed it when I put the Vortex bubble level on and aligned it to the turret. When I put the reticle on the door jab the bubble was buried hard left. So I thought maybe the bubble was not level in its mount so I aligned the windage turret up with the door jab and the bubble was perfectly level, but the reticle was canted to the left of vertical as related to the door jab.

I do not know if I am going to send it back or what I am going to do. I have tried to convince myself that it is just me seeing something that is not there, but the more I measure and re-measure the more obvious it is that it is not me. I do know that none of my other scopes have this issue from various other manufactures.

What did you end up doing Felixx?

 

[joeycoates]

Measured at about .3-.4 degree so I am not going to mess with it, not enough to worry about.

 

[Crashman1]

It could be machining tolerances on the turret cap itself. I always use a plumb bob at about 40-50 yards to level up my reticle and then check the run out by turning the elevation turret up and down on the plumb bob to see how the true the tracking is. My PST has the tiniest amount of run out from the bottom all the way to the top of the adjustment range, about half the reticle width on one side at the bottom to half a reticle width on the other side at the top of the adjustment range. My Razor HD is absolutely perfect, and has been checked several times for this by me and other much better shooters and techs than myself. Any internal error in my PST can not be seen by me at distance because I am just not that good of a shot, and as another poster said even the smallest amount of error in your hold or movement when the shot breaks will have a greater effect on the point of impact.

 

[joeycoates]

I agree, not worth messing with. I plan to check using plumb bob, but it has been so windy and cold here past few days I would have hard time just keeping plumb bob in the reticle! One way or another I highly doubt it would be enough to worry about if even there. You are correct that it could be that the windage knob is not a very good measure of vertical. I will look into it further when I get the opportunity but am happy for now.

 

[SidecarFlip]

I don't want to sound condescending but, the levels you use probably aren't accurate in the first place. Keep in mind that checking errors are only as good as the initial accuracy of the first measurement and all subsequent measurements will compound by the inaccuracy of that initial measurement.

Consequently, I use levels that are accurate to within 0.005" per foot of lineal distance. That ain't a box store, internet gun supply house level. Those are very expensive machinery levelling levels, like 500 bucks each, with precision etched vials and lapped bases. If the indicator bubble(s) are centered, thats good enough for my eyes.

..and yes, all reticles can vary a few degrees from true vertical, thats a result of mass production and human error, no matter how much or little the scope costs.

 

[bruce_ventura]

Measured at about .3-.4 degree so I am not going to mess with it, not enough to worry about.

A reticle alignment error less than 0.5 degrees will not produce a significant aiming error, even at long range. That's easy to confirm using a ballistics calculator.

I regularly see reticle alignment errors of a over a degree. At 2 degrees the aiming error is becomes significant, and is comparable to spin drift.

If you're dialing elevation, then the anti-cant indicator should be aligned to the turret axis instead of the reticle. Then a small reticle misalignment really doesn't matter that much. As Crashman1 said, the best way to check that the elevation turret is plumb is to run the elevation turret up and down while looking through the scope at a plumb line. If the reticle moves left or right off the plumb line, the turret axis is not plumb. The rifle has to be held in a rigid vise when doing this.

 

[joeycoates]

Thanks guys, pretty much what I figured as well. I would like to have a very accurate level, but I do not have machining equipment (although I would like to a some point) so for now I honestly would not have just a whole lot of use for it.

 

[SidecarFlip]

Thanks guys, pretty much what I figured as well. I would like to have a very accurate level, but I do not have machining equipment (although I would like to a some point) so for now I honestly would not have just a whole lot of use for it.

LS Starrett, Brown and Sharpe and Mitutoyo all produce high precision levels in analog (spirit vials with ground graduations) and digital master precision levels.

Typically, the analog levels are accurate to within 0.005" per foot od lineal measurement and the digital master levels will be accurate and repeatable to 0.001 per lineal foot.

The easiest way to ascertain if your level (or any level for that matter) is actually indicating properly is to place the level on a hard surface (like your countertop in the kitchen). It don't have to be square and level, it just needs to be smooth.

Place the level (any level) on the countertop and note the position of the bubble in relationship to the marks indicating the bubble is centered. The swap the ends 180 degrees (1/2 revolution) with the level comong to rest in the same exact spot on the countertop. Note the position of the bubble again in relationship to the marks. Any deviation of the bubble in relationship to the marks is how much the level is 'unlevel'.

You want to have the bubble centered between the indicating marks at the original position (of the level) and rotated 180 degrees. If it's not, the level will never give you a true indication of level or squareness as it relates to vertical plumb..... and the amount of deviation multiplies the error each time a secondary measurement is ascertained (like I stated in a previous post).

I regularly check my precision machinist levels using this method. All machinist levels are adjustable, that is the vial and it's carrier are mounted to the base in a manner that alloows you to adjust the vial to obtain repeatability.

Even a cheap, box store, cemented in vial can be adjusted, it just becomes more complex, either you release the vial from the cement and recement it with paper shims or you machine the base of the level by careful filing.

Always good to check, espceially a cheap box store level because chances are, it's not level in the first place.

You might think that door jamb is square (in relationship to the floor) but is it really? If you never checked the level when the jamb was installed, chances are it's not........

Gravity never lies......lightbulb

BTW, in essence, thats how you 'tram' the spindle on a vertical milling machine to square the z axis to the x and y axis in relationship to the working surface. Thats neither here nor there however.

 

[Freedom2live]

Interesting

 

[wstanton]

Ya I agree, very interesting read! This is a great question, and I am learning a lot, guess its time for me to upgrade my levels....... Or have my smith use his....