Scope adjustment to zero - how much is too much?

[clover]

Considering the apparent issues I've had with my .223 recently has made me re-examine the whole setup and got me thinking about the zeroing. 

The setup is a Sightron SIII 10x42 sat on a Tikka T3x Varmint courtesy of a pair of extra-low Optilocks. The scope was bought used but had had very little use and was apparently still optically centred - "confirmed" both by centring between the extremes of turret adjustment and the fact that both turrets were both set to "0"; their removal confirming only one set of witness marks on the bosses beneath the knobs; suggesting they'd not been moved since new. Both rifle and mounts are new.

Everything was bolted together, the ring caps left loose(ish), the crosshair aligned to the bore with a plumb-line and spirit level on the action (visually confirmed as the vertical crosshair passes through the bore) and the gun bore-sighted then zeroed at 100yd.

In total bore sighting and zeroing required about 32 minutes /  a shade under 10 mils on each axis - not a huge deal as the scope has a generous 75 minutes in each direction, but it still seemed like a lot to me. 

The mounts are around 125mm apart so (if I'm doing my maths correctly) were this discrepancy due to an alignment problem between them, this would suggest an offset of around 1.25mm - which is enormous! 

I've not checked everything meticulously yet but there are no obviously mis-aligned parts - the barrel is straight in the channel in the stock, neither of the mounts seem visibly skewed. In use there appeared to be no windage deviation at extended range. 

I'm not at all concerned about the vertical misalignment as it plays to my advantage since the scope had to be adjusted down to zero; maximising the vertical adjustment I have available for longer targets. I'm less happy about the scope being 50% into its windage adjustment range though.

Does this seem like an acceptable amount to have to adjust the scope to zero? If not, can anyone suggest what might be the cause and how I might check?

Thanks!

 

[Re-Pete]

This is interesting........on my Tikka M595, in order to get the windage aligned with the scope optical centre, I had to shim the rear mount with a sliver of 0.5mm brass.

As I also use Optilocks, this won't place uneven stress on the scope. The sliver is 2mm x 20mm, and it's slid under the fixed side of the Optilock between the claw and the dovetail, moving the rear Opti to the left......see pic (you can also see the shim between the ring and base that adds approx 20 moa to the receiver dovetail)

No matter how much money is spent on scope mounts, unless the rings are lapped parallel  on the pic rail or the dovetails, the only way to ensure even pressure on the scope body is to use Optilocks or Burris Zee Signature rings ..........the Burris area lot cheaper, and better IMHO because they're supplied with a pair of additional offset inserts which enable aligning the scope perfectly to compensate for inaccuracies in the machining without resorting to shimming bodges.

Re-Pete

[clover]

On 8/26/2018 at 8:36 PM, Re-Pete said:

This is interesting........on my Tikka M595, in order to get the windage aligned with the scope optical centre, I had to shim the rear mount with a sliver of 0.5mm brass.

As I also use Optilocks, this won't place uneven stress on the scope. The sliver is 2mm x 20mm, and it's slid under the fixed side of the Optilock between the claw and the dovetail, moving the rear Opti to the left......see pic (you can also see the shim between the ring and base that adds approx 20 moa to the receiver dovetail)

No matter how much money is spent on scope mounts, unless the rings are lapped parallel  on the pic rail or the dovetails, the only way to ensure even pressure on the scope body is to use Optilocks or Burris Zee Signature rings ..........the Burris area lot cheaper, and better IMHO because they're supplied with a pair of additional offset inserts which enable aligning the scope perfectly to compensate for inaccuracies in the machining without resorting to shimming bodges.

Re-Pete

Thanks - that's very interesting indeed!

Sadly for me I'd need a bit more than 0.5mm shim! I've now measured the centres of the rings at a shade under 100mm so to get the (let's round it to) 10 mil I'd need to add a 1mm thick shim. What I'd not considered was shimming the mount for elevation - a nice answer to the only reason I'd ever have bought a Picatinny rail over the optilocks (an angled rail). Very glad I didn't take this route now!

I totally agree about the advantages of the Optilocks and wasn't aware of the Burris equivalents. Two of the big draws to the OEM mounts were the ability of the plastic ring bearing to both centre the scope correctly in the rings as well as protecting the tube.

I've given the rifle a once-over tonight and nothing seems overtly amiss; bases seem dimensionally similar (the front one is maybe 0.2mm shallower but this might be intentional) but no glaring issues in a windage sense. I've visually checked the barrel with respect to the receiver; at around 500mm long it'd have to be skewed with respect to the receiver to the tune of 5mm along its length to cause the windage issue I'm experiencing; which it's clearly not (thankfully!).

I've also checked the scope's objective with a straight edge and it's not bent. I tried the "mirror" approach to checking its optical centre, but it's too dark / the exit pupil too small to see anything.  I suppse there is always a chance that the scope was never properly optically centred as I've not checked it myself in a proper rig, although cranking it from one extreme to the other seemed pretty conclusive.

It's also crossed my mind that I could start reversing / swapping the rings on the bases to see if there's any offset in them (tbh I think it's highly unlikely), although this would be a crushingly tedious task. I do have a laser sight I could sling under the barrel to make the whole process a bit more intuitive and precise than bore-sighting.

Having recently had the function of a pair of windage-adjustable Leupold rings explained to me I do like the idea of drilling and tapping the rear base either side of the ring mounting screw and elongating the screw / ring hole across the base by a few mm; this would allow everything to be assembled finger-tight then the gun bore-sighted by jacking the rear ring across the mount to get the windage somewhere close before it was all tightened up. Can't bring myself to butcher a set of bases though; given how pricey they are and how scarce the stainless ones are becoming!

Could be a nice aftermarket alternative to the Optilock bases to be used with the original rings, though..

Anyway, thanks again for your input - going to have a think about how much I want to pull everything to bits again!

[ejg223]

Thank god I got rid of all my optilocks . Never had issues with pica rails and even 6$ Sun Optic mounts are more reliable and straighter than optilocks.

edi

[onehole]

Optilock rear mount on sako 75,s and possibly 85,s has been a problem for ages,,,,,,,,most don't even know it and just wind in the error!!!,,,,,,The recoil or stop pin is the problem and shimming as above can cure it or remove the stop pin .....but this usually allows the base to forward over travel the chevron dovetail and looks aweful!!......Personally I don't mind fettling the opilocks as you can shim for perfection but for most this would be far to much hassle,,,shimming dovetails is probably beyond most,,,,,,

Going back to OP ,,,,,,,I run RPA,s and Tier One rails and mounts ,,,generally speaking this is good gear and with pretty much "centered NF scopes" have never seen more than 4 to 8 MOA to get a horizontal zero at 100 and that's with fitted moderator.Quite acceptable I reckon ,,,,just as well any shimming would bend something!!!!!,,,,,,,,,,,,,,,,,O 

[Re-Pete]

Am I right in thinking the Sako dovetails are tapered, slightly wider at the rear, or is it the front?.................that sounds like a recipe for disaster to me.

Re-Pete

[onehole]

2 hours ago, Re-Pete said:

Am I right in thinking the Sako dovetails are tapered, slightly wider at the rear, or is it the front?.................that sounds like a recipe for disaster to me.

Re-Pete

75,s and 85,s are ,,,not sure of other models both old and new?,,,,wider at the front on both front and rear dovetails...Not a problem really as the direction provides a secure anti recoil situation. The problem is that unless the mounts are allowed to fully engage with the taper then on tightening the mounts they will pull toward the locking lug and off centre to the action, The front mount generally does not cause a problem as you can usually push it well forward ,self centre and tighten but the rear will almost without exception pull out of line and force users to crank in sometimes huge amounts of windage to correct.No damage to scopes will  occur as the ring inserts will run with any misalignment but not correct the issue.... I can live with this issue given these rifles are off the shelf consistently very very accurate and there are a  ways to get around it and have your scope zeroed and working from a near centred reticule.,,,,,,,,,,,,O

[clover]

18 hours ago, Re-Pete said:

Am I right in thinking the Sako dovetails are tapered, slightly wider at the rear, or is it the front?.................that sounds like a recipe for disaster to me.

Re-Pete

Indeed they are - tapered towards the rear to prevent the mounts creeping forward under recoil I imagine.

On 8/28/2018 at 11:58 PM, onehole said:

Optilock rear mount on sako 75,s and possibly 85,s has been a problem for ages,,,,,,,,most don't even know it and just wind in the error!!!,,,,,,The recoil or stop pin is the problem and shimming as above can cure it or remove the stop pin .....but this usually allows the base to forward over travel the chevron dovetail and looks aweful!!......Personally I don't mind fettling the opilocks as you can shim for perfection but for most this would be far to much hassle,,,shimming dovetails is probably beyond most,,,,,,

Going back to OP ,,,,,,,I run RPA,s and Tier One rails and mounts ,,,generally speaking this is good gear and with pretty much "centered NF scopes" have never seen more than 4 to 8 MOA to get a horizontal zero at 100 and that's with fitted moderator.Quite acceptable I reckon ,,,,just as well any shimming would bend something!!!!!,,,,,,,,,,,,,,,,,O 

 

15 hours ago, onehole said:

75,s and 85,s are ,,,not sure of other models both old and new?,,,,wider at the front on both front and rear dovetails...Not a problem really as the direction provides a secure anti recoil situation. The problem is that unless the mounts are allowed to fully engage with the taper then on tightening the mounts they will pull toward the locking lug and off centre to the action, The front mount generally does not cause a problem as you can usually push it well forward ,self centre and tighten but the rear will almost without exception pull out of line and force users to crank in sometimes huge amounts of windage to correct.No damage to scopes will  occur as the ring inserts will run with any misalignment but not correct the issue.... I can live with this issue given these rifles are off the shelf consistently very very accurate and there are a  ways to get around it and have your scope zeroed and working from a near centred reticule.,,,,,,,,,,,,O

Thanks - I'm glad you've had success with your setup!

That's somewhat concerning about the Optilocks - if nothing else they're certainly divisive!

So the recoil pin limits the forward travel of the rear mount, meaning it's sloppy on the tapered dovetail and gets pulled to one side when it's tightened? If so that seems like a pretty schoolboy error to me.. I really don't see why the setup needs both tapered dovetails and a recoil stud (nor how these can correctly work together) given only one can limit fore/aft movement of the mount on the gun.

To be honest I can't see the advantage of the tapered mounts used by Sako - seems like a lot of extra work for a system that's inferior to a parallel dovetail and arrestor stud. Presumably it limits your choice of scope position too, since the mounts can effectively only fit in one location. I'm sure shimming can be effective, but really shouldn't be necessary!


I revisited my situation today and thankfully it appears to be the result of my own oversight

From their zeroed (to the rifle) position I cranked the turrets to the extremes of their travel in each direction; the resultant displacements being:

Left / Clockwise: 75.0 MOA
Right / Anticlockwise: 79.0 MOA
Down / Clockwise: 74.5 MOA
Up / Anticlockwise: 79.0 MOA

So assuming this method can be relied upon to give an approximation of the scope's optical centre, at worst the scope is 2.25MOA off centre - I can live with that!

This also suggests that the scope has a shade more total internal adjustment than advertised (150 MOA) although I didn't check that the ret was actually moving when adjusted at the extremes of its range. Chances are I should never have to go out this far anyway. On paper that's enough elevation adjustment to take me past 1000yds; although I doubt I'll be trying since I can't hit anything at 600..

I was sure I'd carried out this test before I zeroed the scope, but was evidently mistaken. It seems that the previous owner must have re-zeroed the turrets and over-tightened their retaining grub screws a little - hence the single set of witness marks when the turrets were removed.

Yet another example (as if one was needed) of why it never pays to make assumptions.

Thanks for everyone's input!


 

[Davy]

A good way of telling if your 'scope is on its mechanical zero or not is to place a mirror in front of the objective allowing just a little light in, you will see your reticle plus a 'ghost reticle' align the two using the turrets and you are on the true zero across the horizontal and vertical axis. You can now bore sight and either zero using the bases if using Apel or similar or alternatively take a shot and see just how far you are out at a known distance.

Zeroing the 'scope in such a manner is very handy for the multi turn turrets, especially if you are working with a pre-owned model.

On the subject of Optilock, I am yet to find one that is significantly out and I recently had a Sako 75 .243 out for zero having zeroed the 'scope as described, it was a very still day and first shot was 3-4mm from the vertical, which for a mass produced rifle with so many variables was rather good.

[VarmLR]

I'd second the Burris Zee Signature rings for ensuring proper alignment. They're a very elegant and well made engineering solution.  I've been using them in the newer Zee Tactical Signature Extreme guise for a while now on a TAC A1 and don't recall having to dial much, if any, windage allowance to zero.  They have the added advantage that whilst they will not increase overall scope adjustment range, they do allow vertical and horizontal offsets whilst maintaining proper scope barrel alignment without any consideration to lapping.  From memory, vertical alignment offset can be as much as 40 or 45moa using these so they will get many rifles out a very long way! I have mine set at 20moa increase in place of using a 20moa rail, and am easily able to maintain a 100yd zero (PMII).   

There are other options available, such as the more expensive fully adjustable one piece mounts on offer like the ERA-TAC model manufactured by Recknagel.  These have advantages that any slight errors on your dovetail mounts can effectively be dialled out to allow perfect alignment of the scope, and whilst they can be dialled for acheiving POI, they're designed more as a dial to compensate for error then lock-off solution.  They still though have the added advantage that they also offer various degrees of elevation increase...more than enough to get some rifles out beyond 2000 yards and unlike other moa solutions, this type can offer increased moa range, not just a lift in zero with no moa range increase. There's a USA based company selling the best one I've seen that claims to allow a 100yd zero but then you can use the mount to dial you out to 3/4 off a mile!  Can't recall the name but a guy at one of my clubs has one.

The Sako mount design issues just smacks of creating several new problems to solve something that other manufacturers don't see the need for by going to tapered dovetails, and the alleged machining errors on the stop-pins doesn't engender any confidence if true.  It all seems to add up to a Heath Robinson solution to a problem that wouldn't exist with a little more thought and care in design and manufacture.

My money would be on the scope being fine and the real issue more than likely the standard Sako mounting system.  As above, the good news is that there are plenty of solutions.  I think the Zee Siggy Extremes cost me around £120

[clover]

Thanks for the thoughts chaps - although as per my previous post I've now got to the bottom of the issue

On 8/30/2018 at 1:36 PM, Davy said:

A good way of telling if your 'scope is on its mechanical zero or not is to place a mirror in front of the objective allowing just a little light in, you will see your reticle plus a 'ghost reticle' align the two using the turrets and you are on the true zero across the horizontal and vertical axis. You can now bore sight and either zero using the bases if using Apel or similar or alternatively take a shot and see just how far you are out at a known distance.

Zeroing the 'scope in such a manner is very handy for the multi turn turrets, especially if you are working with a pre-owned model.

On the subject of Optilock, I am yet to find one that is significantly out and I recently had a Sako 75 .243 out for zero having zeroed the 'scope as described, it was a very still day and first shot was 3-4mm from the vertical, which for a mass produced rifle with so many variables was rather good.

I did try the mirror trick but the particular scope in question was too dark / had too-small-an exit pupil for this to work.

After I took the time to double-check the scope's optical centre my experiences with the optilocks were similar to (if not quite as good as) yours; at around 2.25 MOA max deviation from optical centre  

On 9/2/2018 at 6:11 AM, VarmLR said:

I'd second the Burris Zee Signature rings for ensuring proper alignment. They're a very elegant and well made engineering solution.  I've been using them in the newer Zee Tactical Signature Extreme guise for a while now on a TAC A1 and don't recall having to dial much, if any, windage allowance to zero.  They have the added advantage that whilst they will not increase overall scope adjustment range, they do allow vertical and horizontal offsets whilst maintaining proper scope barrel alignment without any consideration to lapping.  From memory, vertical alignment offset can be as much as 40 or 45moa using these so they will get many rifles out a very long way! I have mine set at 20moa increase in place of using a 20moa rail, and am easily able to maintain a 100yd zero (PMII).   

There are other options available, such as the more expensive fully adjustable one piece mounts on offer like the ERA-TAC model manufactured by Recknagel.  These have advantages that any slight errors on your dovetail mounts can effectively be dialled out to allow perfect alignment of the scope, and whilst they can be dialled for acheiving POI, they're designed more as a dial to compensate for error then lock-off solution.  They still though have the added advantage that they also offer various degrees of elevation increase...more than enough to get some rifles out beyond 2000 yards and unlike other moa solutions, this type can offer increased moa range, not just a lift in zero with no moa range increase. There's a USA based company selling the best one I've seen that claims to allow a 100yd zero but then you can use the mount to dial you out to 3/4 off a mile!  Can't recall the name but a guy at one of my clubs has one.

The Sako mount design issues just smacks of creating several new problems to solve something that other manufacturers don't see the need for by going to tapered dovetails, and the alleged machining errors on the stop-pins doesn't engender any confidence if true.  It all seems to add up to a Heath Robinson solution to a problem that wouldn't exist with a little more thought and care in design and manufacture.

My money would be on the scope being fine and the real issue more than likely the standard Sako mounting system.  As above, the good news is that there are plenty of solutions.  I think the Zee Siggy Extremes cost me around £120

From a design perspective I too like both the Burris and Sako/Tikka rings - the plastic inserts being one of the main reasons I chose the Optilocks, although admittedly they don't have the adjustability of the signature rings. As Re-pete suggests above it's quite straightforward to shim the Optilocks; certainly for elevation without much fuss. With mine spaced at 100mm for every 0.1mm of shim thickness added between the rear base and ring I'd get 1 mil of elevation adjustment - so 20MOA could be achieved with around 0.6mm of packing.

I'm a fan of the old B-Square fully adjustable mounts and have numerous sets on my air rifles; great for getting the scope pointing where it should be but tbh I'd not trust any mount to be precise enough to adjust on the fly for range correction. Bet those that can be aren't cheap!

I do agree about the Sako mount setup though - the design actually puts me off buying a Sako (not that I ever would anyway as their LH selection is pretty pitiful) and I consider the straight dovetails and recoil pin setup on the Tikka far superior; while also a lot cheaper and easier to machine.