Good Scope Mounting Tools

[gunner69]

This is a statement about vertical and horizontal aiming error, not canting error. Yes, it is true that an aiming offset of 1 MOA produces an aiming error of 10" at 1,000 yds. I don't see how that's relevant to this discussion, which is about cant error.

Aiming errors due to scope canting are much smaller – by about a factor of 100. For most long range hunting calibers, the aiming error at 1,000 yds is roughly 10" for 120 MOA (or 2 degrees) of cant angle. You haven't convinced me why anyone actually needs 1 MOA precision when aligning a scope reticle.

I've found that aligning the scope to within +/-15 MOA of plumb is routinely possible with a little care. This is the typical accuracy of the HPO Reticle Alignment Tool (it's guaranteed to have an error less than +/-30 MOA). I normally don't use any other levels or plumb lines when I install a scope and anti-cant indicator. In my experience, however, holding the cant error to +/-15 MOA in the field is not easy to do. Holding cant angle to within +/-30 MOA is a more realistic goal. For long range hunting calibers, +/-30 MOA of cant error limits the aiming error to roughly +/-3". Of course, this error will vary depending on the caliber.

The aiming error due to not aligning the scope to the rifle bore is roughly +/-2" at 1,000 yds, although it varies a lot from one rifle to another. Using the Reticle Alignment Tool will eliminate this error.

Proper use of an anti-cant indicator will then allow an experienced shooter to achieve an aiming error of less than +/-3" at 1,000 yds (neglecting wind effects of course) without a lot of effort. Most long range shooters would be satisfied with this aiming accuracy, given that wind estimation error is usually a bigger problem. While it's possible to get even better accuracy, I think it requires a fair amount of experience aligning scopes and shooting with an anti-cant indicator.


Most of the shooters on this forum are mainly interested in making the long range shot, not in scope alignment methods. For them preventing canting errors in the field is the primary objective of aligning a scope. Accurate scope alignment is not the end goal for them, it is just the means to the end, and it's really only half of the problem. How one holds the rifle to prevent canting errors in the field is the other half of the problem.


This is only true for holding elevation, not dialing elevation. How one deals with a misalignment between the reticle and the turret axes depends a lot on how the scope is being used. For 1,000 yd shots, I think that shooters generally prefer to dial elevation. If there is an angular misalignment between the reticle and the turret axis, and the reticle is plumb during the shot, an aiming error a will be introduced when dialing elevation, but not when holding elevation.

The reason is simple: if the turret axis is not plumb, then dialing elevation also introduces a small windage offset. This is simple geometry and many people, including myself, have confirmed this at the range.

So, my basic rule is: when dialing elevation, align the turret axis; when holding elevation, align the reticle. That way a misalignment between the reticle and the turret axis won't cause a canting error.

I almost can't even begin to know where to start so I'll just simply say this to keep it super simple. 1. The reticle must always be alligned to a plumbline that is alligned with earths gravity ie a rope with a weight on it hanging (free of movement). 2. The alligned reticle is most effective to the shooter when mounted atop a level rifle. A level rifle is one where a reference point ie bolt races or scope rail are 100% level agian using earth as the reference point. Then and only then has the shooter eliminated built in cant issues and can focus on the other difficulties of making long range shots.

 

[woods]

Bruce or woods,
Explain how to "align the turret axis" and confirm alignment in a straightforward, efficient manner - preferably without shooting a bunch of ammo? I've improperly presumed a scope turret would track thru its motion parallel with the reticle. But I understand how the mechanical turret movement could be misaligned with the vertical reticle... which would be quite a disappointment to me.

Could a guy secure his rifle/scope in a rifle vise, draw a long vertical/plumbed line on a piece of cardboard, line the vertical crosshair up on the line and crank the scope turret thru its up and down throws and confirm the crosshair intersection tracks up and down the line drawn on the cardboard? I've performed this procedure on all of my long range rigs in order to calculate the true value of my scope turret clicks, by measuring the distance the crosshairs move divided by the number of scope clicks per 100 yards - for a straightforward, measured determination of inches/click/100 yds.

The crosshair on my 3 long range rigs did track parallel with the plumb/vertical line I'd drawn on a large piece of cardboard at 100 yds. I was confirming my scope's click value, but in doing so, I do remember the crosshair intersection also tracked on or parallel to the line on the cardboard. This test would also uncover any tracking misalignment of the turret axis with the vertical reticle - no? Thought or comments?

Phorwath, I can find no fault with your method

This is MY OPINION, worth what you pay for it

gunners equipment is a well built precision instrument. I am not sure that taking the cant out of the rifle by leveling the raceways will always work. And he has made no arrangement for an anti-cant to duplicate the level rifle in the field. Also, procuring such an instrument would be very costly and not for 99% of the posters on this forum.

bruce's less expensive piece of equipment looks well made and well thought out. I am all for entrepreneurs and their products. I would be concerned that there is no alignment of the scope centerline and the bore centerline like the 2 V's on the EXD accomplish. Don't know whether you would be able to gauge that with the vertical lines in relation to the objective of the scope or not.

I have a friend who uses a gunsmith who has a machine that will do all we have talked about

but, there again, it does 99% of us here no good at all

There is another scope mounting tool that is interesting

Parabola LLC » PRODUCT INFO

that many speak highly of

As far as turrets go, I would not trust any of them to be in perfect alignment with the reticles or use any part of the turrets for the leveling process.

One thing for sure is that the it is not necessary to hold the rifle uncanted, only that when you pull the trigger the reticle is level. Example David Tubbs cheek over rifle/scope

 

[bruce_ventura]

Bruce or woods,
Explain how to "align the turret axis" and confirm alignment in a straightforward, efficient manner - preferably without shooting a bunch of ammo? I've improperly presumed a scope turret would track thru its motion parallel with the reticle. But I understand how the mechanical turret movement could be misaligned with the vertical reticle... which would be quite a disappointment to me.

Could a guy secure his rifle/scope in a rifle vise, draw a long vertical/plumbed line on a piece of cardboard, line the vertical crosshair up on the line and crank the scope turret thru its up and down throws and confirm the crosshair intersection tracks up and down the line drawn on the cardboard? I've performed this procedure on all of my long range rigs in order to calculate the true value of my scope turret clicks, by measuring the distance the crosshairs move divided by the number of scope clicks per 100 yards - for a straightforward, measured determination of inches/click/100 yds.

The crosshair on my 3 long range rigs did track parallel with the plumb/vertical line I'd drawn on a large piece of cardboard at 100 yds. I was confirming my scope's click value, but in doing so, I do remember the crosshair intersection also tracked on or parallel to the line on the cardboard. This test would also uncover any tracking misalignment of the turret axis with the vertical reticle - no? Thought or comments?

Yes, this test should work as you described if the rifle is held in a vise rigidly enough that the point of aim doesn't shift when handling the turret. I use a different method. It requires a custom alignment tool that is still in product development, but the optical geometry is essentially the same.

If the scope has a flat machined surface on the turret housing, it should be square with the turret axes. I reference off that surface using an accurate level. Then the turrets should be plumb to within the accuracy of the level. When I view the plumb line through the scope, I can immediately tell if the reticle is square with the turrets or not.

I assume you plan to use your rifles in the field, and not just on a bench. If so, I would attach the anti-cant indicator while the rifle is still in the vise.

 

[Pdvdh]

Phorwath, I can find no fault with your method.

One thing for sure is that the it is not necessary to hold the rifle uncanted, only that when you pull the trigger the reticle is level. Example David Tubbs cheek over rifle/scope

David Tubbs cheek Say WHAT??? That's quite the contraption.

Thanks for your feedback woods. I did run my vertical turret through about 40" of movement at 100 yds, as I recall. Maybe 20" above POA and 20" below point of aim. All three of my Sightron SIIIs tracked in alighnment up and down, parallel with the vertical crosshair and the vertical line drawn on the cardboard. That seems evidence enough to me that at least those three scopes have vertical turret motion parallel to their vertical crosshairs - at least as close as I could observe on the 100 yd target.

 

[Pdvdh]

I assume you plan to use your rifles in the field, and not just on a bench. If so, I would attach the anti-cant indicator while the rifle is still in the vise.

Thanks for sounding in Bruce. Yes my rifles are hunting rifles - backpack hunting. So 10-4 on the anti-cant devices. They are mounted after everything has been plumbed to gravity. After mounting the scope and squaring everything up, including the anti-cant, is when I then headed out to calculate my vertical turret movement per click per 100 yds. I wasn't trying to confirm turret tracking with the vertical reticles at the time, but I do know that they tracked up and down with the vertical line on my cardboard target which was also in alignment with my vertical cross hair. If the tracking had deviated noticeably, I'd have been scratching my head.

Paul

 

[bruce_ventura]

...bruce's less expensive piece of equipment looks well made and well thought out. I am all for entrepreneurs and their products. I would be concerned that there is no alignment of the scope centerline and the bore centerline like the 2 V's on the EXD accomplish. Don't know whether you would be able to gauge that with the vertical lines in relation to the objective of the scope or not...

Actually, using the vertical lines on the Reticle Alignment Tool to center the scope objective works very well. That's because this part of the alignment process does not require high precision, as long as the alignment is done at the objective end of the scope. The purpose of this part of the process is to prevent relatively large horizontal offsets (>0.1") between the scope tube and the rifle bore.

The geometry is simple: a 0.1" horizontal offset produces a 0.9" aiming error at 1,000 yds (assuming a 100 yd zero). For most shooters, that's acceptable aiming accuracy. Using the lines on the tool to center the scope tube easily allows alignment to within 0.1".

Doing this alignment at the eyepiece end of the scope (aligning the eyepiece to the rear of the receiver) is prone to errors when the barrel isn't boresight aligned with the receiver. I frequently encounter production rifles that have barrels installed crooked in the receiver. In that case, the rear of the receiver can be offset horizontally from the barrel axis.

The second part of the alignment process requires a spirit level that is accurate to within +/-15 MOA, and that is the tolerance to which the Reticle Alignment Tool is assembled. So, the tool is designed to provide the level off accuracy and precision needed, while keeping the cost down.

 

[gunner69]

I almost can't even begin to know where to start so I'll just simply say this to keep it super simple. 1. The reticle must always be alligned to a plumbline that is alligned with earths gravity ie a rope with a weight on it hanging (free of movement). 2. The alligned reticle is most effective to the shooter when mounted atop a level rifle. A level rifle is one where a reference point ie bolt races or scope rail are 100% level agian using earth as the reference point. Then and only then has the shooter eliminated built in cant issues and can focus on the other difficulties of making long range shots.

Phorwath, I can find no fault with your method

This is MY OPINION, worth what you pay for it

gunners equipment is a well built precision instrument. I am not sure that taking the cant out of the rifle by leveling the raceways will always work. And he has made no arrangement for an anti-cant to duplicate the level rifle in the field. Also, procuring such an instrument would be very costly and not for 99% of the posters on this forum.

bruce's less expensive piece of equipment looks well made and well thought out. I am all for entrepreneurs and their products. I would be concerned that there is no alignment of the scope centerline and the bore centerline like the 2 V's on the EXD accomplish. Don't know whether you would be able to gauge that with the vertical lines in relation to the objective of the scope or not.

I have a friend who uses a gunsmith who has a machine that will do all we have talked about

but, there again, it does 99% of us here no good at all

There is another scope mounting tool that is interesting

Parabola LLC » PRODUCT INFO

that many speak highly of

As far as turrets go, I would not trust any of them to be in perfect alignment with the reticles or use any part of the turrets for the leveling process.

One thing for sure is that the it is not necessary to hold the rifle uncanted, only that when you pull the trigger the reticle is level. Example David Tubbs cheek over rifle/scope

I paid about $170 for the leveling base, ocular level and plumb line which given the quality I felt was an excellent value. Came all together. Also for shooting at the range and f class the ocular level is super for leveling your rest as well. I don't have a method of leveling the rifle in the field say hunting better than any other method but there is a million anti cant levels already available for your scope.. As far as using the bolt raceways as the reference point, the scope rail can also be used as mentioned especially on custom actions when you can be assured all is machined square etc.