Misaligned scope mount dovetails on new Sako 85 Finnlights

[David_S]

I bought a new Sako 85 Finnlight in 260 Rem a few months ago and temporarily fitted an old Leupold Scope in new Sako Ringmounts whilst I awaited delivery of a Swarovski. I noticed I that I had to make considerable vertical scope adjustment to get the shots on paper at 25yards but was not overly concerned as it was only a temporary arrangement whilst I worked up a load. With the right load the rifle proved very accurate and took its first deer a couple of days ago.

I eventually received the Swarovski a couple of weeks ago and bore sighted it with the crosshairs set at the centre of the scope adjustment range. The crosshairs were approximately 6" high at 25 yards. i.e. 24" high at 100 yds corresponding to 96 clicks on the scope! The Swarovski only has a total vertical adjustment of 172 clicks (86 either side of centre) so there was no way I could mount the scope with the crosshairs anywhere near the recommended centre of range. In fact I could not mount it at all without running out of adjustment.

Now the tapered dovetails on the 85 allow windage adjustment but there is no provision that I can see for vertical adjustment, and no easy way of shimming the Ringmounts. (I had opted for Ringmounts rather than the two-piece base types which can be shimmed easily as they were lighter and cheaper, and this is a lightweight mountain rifle).

The underlying problem is that the rear dovetail is not aligned, or even closely aligned, with the front one as can be seen from this photo.



Is this a common problem with the 85s? It is certainly not an isolated instance as I also have a new Sako 85 Finnlight in 270WSM which has the same problem but not as pronounced. Now how can Sako produce a quality rifle / dovetail / ringmount system which won't mount quality scopes such as Swarovski, Zeiss or Leupold? It has somewhat shaken my confidence in Sako quality assurance.

The logical action was to send both rifles back to Beretta under warranty but I was not prepared to wait whilst I argued it out with Beretta. These are hunting rifles, not wall ornaments, and I want to be out hunting whilst I can - Spring is here! And Beretta could, and probably would, argue that the warranty is technically voided as I have handloaded both rifles, though this has nothing to do with misaligned dovetails. In any case both rifles shoot well and have the factory set triggers fitted so I want to hang on to them.

I have, in fact, found a way to shim the Ringmounts on both rifles so that at my 200 yard zero the crosshairs are a little below mid-range, as I want. For the sake of others with similar problems I will post the details when I have a moment.

Has anyone else had this problem? And what did you do? Or am I missing something obvious?

David

 

[kevinlg]

David,

You're only concerned about vertical alignment.......correct?

Have you checked alignment with the barrelled action removed from the stock?

Are the dove-tail groove bottoms also out of alignment?

I usually use a machinists 6" rule, on edge, to check the flats tops. What are you using?

Your pic appears to show that the rear receiver ring is lower than the front receiver ring. Is this correct? If so.......well..........your rifle "should" be shooting low.....not high.

Interesting problem........but, more information is needed.

Hope this helps....

 

[David_S]

Kevin, thanks for your reply. Here is the info you wanted.

You're only concerned about vertical alignment.......correct? Yes, moving the front mount forward or back adjusts the scope laterally so it is easy to get the windage reticule close to the centre of its range.

Have you checked alignment with the barrelled action removed from the stock? No. Not sure what this would achieve as both dovetails are an integral part of the action

Are the dove-tail groove bottoms also out of alignment? I have not checked this as the mounts sit on the flat top and the clamps grip the upper lip of the groove. In fact the mount position is determined by the upper lip rather than the flat top as there is a very small clearance between the bottom of the ringmount and the dovetail top.

I usually use a machinists 6" rule, on edge, to check the flats tops. What are you using? I used a 6" steel square but for the picture used the flat centre strip of vernier calipers. I could not hold the square and take the photo at the same time!

Your pic appears to show that the rear receiver ring is lower than the front receiver ring. Is this correct? If so.......well..........your rifle "should" be shooting low.....not high. That's right. When bore sighted the crosshairs were high so when the crosshairs are on target the bore is lower and the rifle shot low - very low!

Interesting problem........but, more information is needed.

I will post details of how I shimmed both rifles tomorrow. It's rather late at the moment and I need to take some pictures. In the end I put the Swarovski on the 270WSM and the Zeiss on the 260. The Swarovski has Ballistic Turrets so it was important to ensure that my zero was close to the centre of the available vertical adjustment. I also have a 75 Finnlight in 270 WSM with a Zeiss scope and Sako Ringmounts mounted by a previous owner so when I have the 85 WSM sorted it will be interesting to see if the 75 has the same problem as the 85s.

David

 

[sako 22 250]

Kevin, thanks for your reply. Here is the info you wanted.

You're only concerned about vertical alignment.......correct? Yes, moving the front mount forward or back adjusts the scope laterally so it is easy to get the windage reticule close to the centre of its range.

Have you checked alignment with the barrelled action removed from the stock? No. Not sure what this would achieve as both dovetails are an integral part of the action

Are the dove-tail groove bottoms also out of alignment? I have not checked this as the mounts sit on the flat top and the clamps grip the upper lip of the groove. In fact the mount position is determined by the upper lip rather than the flat top as there is a very small clearance between the bottom of the ringmount and the dovetail top.

I usually use a machinists 6" rule, on edge, to check the flats tops. What are you using? I used a 6" steel square but for the picture used the flat centre strip of vernier calipers. I could not hold the square and take the photo at the same time!

Your pic appears to show that the rear receiver ring is lower than the front receiver ring. Is this correct? If so.......well..........your rifle "should" be shooting low.....not high. That's right. When bore sighted the crosshairs were high so when the crosshairs are on target the bore is lower and the rifle shot low - very low!

Interesting problem........but, more information is needed.

I will post details of how I shimmed both rifles tomorrow. It's rather late at the moment and I need to take some pictures. In the end I put the Swarovski on the 270WSM and the Zeiss on the 260. The Swarovski has Ballistic Turrets so it was important to ensure that my zero was close to the centre of the available vertical adjustment. I also have a 75 Finnlight in 270 WSM with a Zeiss scope and Sako Ringmounts mounted by a previous owner so when I have the 85 WSM sorted it will be interesting to see if the 75 has the same problem as the 85s.

David

Hi David
I have a model 85 varmint in 22 -250 with a Zeiss Duralyt 3-12 x 50 scope

When I went to pick up the new rifle & scope and optilock ring and bases (30 mm high) from the gunshop. The optllocks I had ordered had gone missing ...the gunshop lent me a set of Sako dovetail ring mounts
( 30 mm medium ) until a new set of optllocks arrived .
Interestingly with these ring mounts I only had 2cm adjustment left (up) when zeroed at 100m on the Zeiss .... this did concern me !
Once replaced with the optliock ring and base set this was no longer a issue
Currently I have the rifle zeroed at 3 cm high at 100m this leaves me adjustment of 21 clicks up and 27 clicks down ( Duralyt is 1cm per click @ 100m)


I could not be happier with this set up its one very accurate rifle

Hope this helps
Regards Mark

 

[kevinlg]

David,

Sorry about the high/low thing......my mistake.

But......the reason for checking the action top flats, with the barrelled action out of the stock, is because the stock may flex the action if something is not quite right with the stock bedding.

It's odd.....because I've never seen Sako action top flats be so far "off". But, I've never owned a Sako 85.


Another check is to put the "straight edge" on the rear flat.....and slide forward. If it ends up over the front flat....the action is "flexed".

 

[cmjr]

My question is are the 85 bridges supposed to be at the same height? If so and yours are not box that baby up and get her on the way back to Sako land, those rifles cost too much to deal with a problem like that. Almost sounds like they are not the same height and will need ring bases specific to the model.

 

[paulsonconstruction]

I'll bet a dollar to a nickel that the problem is NOT the Sako dovetails. Try a different set of mounts! The difference in dovetail height would make the POI low not high. Something doesn't add up here. Can't imagine a CNC'd receiver being mis-machined & leaving the factory. No way a screw could "flex" an action to that degree when wood is the bearing surface. Flexing of an action is hardly measurable & wouldn't be perfectly level as in the pic. You couldn't put enough torque on a screw with hand tools to "bend" an action that much. Will be curious as to the resolution.

 

[David_S]

Thanks everyone for your replies. I will try to answer your points/queries and add a few further observations.

1) Sako 22-250. Mark, this sounds as though it is exactly the same problem as I have encountered. And yes, two-piece optilocks would correct the problem as they can be shimmed with the "traditional" beer can shims. We did this with the M995 when we set it up for long-range shooting with a Sightron 6-24 x 42 scope. However, as I mentioned before, I did not want to use the two base optilocks to keep the weight down and also to maximise the distance between the mounts.

2) Kevinlg I have not taken the barrelled action out of the stock on either 85 or the 75. I did not see any need to do that with factory new rifles. And as Paulsonconstruction notes it would take more than screw pressure to bend the action to such an extents as shown in my photo.

I also did the check you suggested of sliding the straightedge from the rear to the front. It hit the front about 0.8mm low as I expected. Incidentally the rear dovetail does appear to slope slightly as shown by these measurements




and if you do the maths on these measurements you get a difference of 16.8 MOA between the front and rear mount positions which is pretty much what I found when I bore-sighted the rifle.

3) cmjr Yes I am assuming that the bridges are supposed to be at the same height. They have to be if Sako Optilock Ringmounts are to be used as there is no difference in elevation between front and rear Optilock rings. Of course it is possible that Sako 85s are not designed to take the one-piece Sako Ringmounts but, if this is the case, it would be nice if Sako were to let new owners know! And as I said before I don't want to send these rifles back and miss out on the "spiker" season which is due to start any day now - my wife wants the freezer restocked!

4) Paulsonconstruction I think I should take that dollar off you now! I have tried two sets of new Optilock Ringmounts on two different new Sako 85s and all four combinations have the same problem. And yes as I explained to Kevin, the rifles were shooting low as with the bore lasersighted on a target at 25 yards the crosshairs were some 6" high. All the measurements I have made point to the problem being that the front and rear dovetails are at different heights. Why, or how this could occur, I have no idea. But it is not an isolated problem as it occurs on both my 85 Finnlights bought last December and in March and also on Mark's 22-250. My 260 and Mark's 22-250 use the 'S' action and the 270WSM the 'SM' action so it is not confined to one action.

I keep thinking I am missing something here as I cannot imagine Sako allowing such height variation between front and rear rails unless it was intentional. Nor in a quality rifle should they be relying on the scope adjustment to compensate for it. No scope and certainly neither my Swarovski nor Zeiss likes operating at the limit of their adjustment.

Here are some photos of the Zeiss mounted on the 260Rem







Edited July 2017 to restore Photobucket images

David

 

[stonecreek]

I agree that both dovetails should be the same height. This looks somewhat as if the computer driving the CNC machine had a hiccup, or someone entered a bad number into it.

The quick fix, which is frequently used when screw-on mount bases are of unequal height, is to simply bush with thin aluminum strips between the scope body and the rear ring. I had to do this with my very first Sako in 1965, not because the dovetails were uneven, but because the Redfield bases were of slightly different heights. That same Leupold is still sitting on that four-digit L61R almost fifty years later and still puts the first shot from a cold barrel dead-on at 100 yards. Incidentally, in my instance the rear base was too high (or front too low, as you will), putting all shots high at maximum scope adjustment.

 

[David_S]

What I finally did!

Well this is what I finally did. I like the Optilock Ring Mounts as they are a solid compact quality mount and I particularly like the spherical inserts which compensate for any ring misalignment without the need for lapping. Lateral adjustment is achieved by sliding the front mount on its tapered dovetail on the receiver which is a neat system. But why is there no provision for vertical adjustment such as a range of off-centre inserts such as Burris use? Beats me.

As an initial experiment, whilst still at the boresighting stage, I tried placing the traditional "beer can" shims between the bottom of the insert and the ring. It required 6 shims plus a layer of protective loom tape (approx 0.8mm total) to bring the rifle to the equivalent of a 200 yard zero. Not a permanent solution. The WSM required 3 shims + loom tape (0.5mm total).

There is no obvious place for permanent shims such as with the two-piece optilocks that I have on my Sako M995. I tried putting shims under the mount on top of the dovetail and this looked as if it might work but I was concerned that this method would not leave enough clamping surface for the mount. On the WSM it required 1.2mm shimming this way. (More than for shimming the insert as there is a gap between the mount and the dovetail to fill first as can be seen in the photo of my earlier post).

My options at this stage were

1. Return rifles under warranty - wait months for a "solution" whilst I should be out hunting.
2. Switch to 2 piece optilocks - extra cost and extra weight
3. Switch to Burris or other rings - Sako ringmounts really don't match Sako rifles??
4. Try the second shimming method above and hope the clamps hold - probably not worth the risk.
5. Make some off-centre inserts - maybe the Burris ones would fit or could be modified

It didn't look as if the Burris ones could be modified so I was about to investigate other rings when I thought of another simpler solution.

I abandoned the idea of shimming the base because of the potential loss of grip and experimented with an epoxy layer between the plastic insert and the bottom half of the ringmount.

I first coated the insert with car wax to act as a release agent, then placed some epoxy in the bottom of the ring and pressed the insert down on the epoxy squeezing it up the sides. After the epoxy set the insert was easily removed and left a near perfect bedding shaped to allow the insert to rotate as designed but seated higher. It is a similar process to bedding an action. The only difficulty was in judging how far out to seat the insert as it was difficult to measure accurately. I just eyeballed it and came pretty close as my boresighting at 25 yards dropped from 10" low to 2". I then sighted it in at 200 yards.

I was tempted to leave it at that but I really wanted to have the crosshairs approximately 25 clicks below the mid-range at my 200 yd zero so that I had plenty of "up" clicks left to go out to 500 yards with the 260/Zeiss or further with the 270WSM/Swarovski. So I redid the epoxy so that I had an excess thickness and then slowly removed the excess until I reached the required thickness. From my 200 yard sighting-in it was simple to calculate what the 25yd boresighted crosshair position should be for the 200yd zero. I had the rifle set up inside on a lead-sled boresighted on a mark outside. With the excess epoxy the crosshairs were now below the mark so I just removed epoxy until the crosshairs moved up into position.

The main difficulty was how to remove the epoxy and still retain the groove for the plastic inserts to swivel in. after a bit of thought I had a special tool made as below to match the inserts and used medium grinding paste to cut the epoxy. This worked well. I had the arms of the tool made out of 30mm dia bar so that if I ever changed to 30mm dia scopes I could use it as a lapping bar. By chance the guy who did the job for me was a keen hunter and owned a Tikka, and again by chance I had a set of Tikka Optilock Ringmounts so we did a straight swap.

I used the same screws as before but, depending on the thickness of the epoxy shim, longer screws might be necessary.

My apologies for the long post but I thought the method might be useful for others with the same problem. I have successfully done both the 260 and the WSM this way and as soon as I have a load for the WSM sorted I will do my Sako 75 if necessary. Any comments/suggestions/improvements welcomed.

David
(Edited July 2017 to restore lost Photobucket images)

 

[kevinlg]

David,

Ok......just to recap.

You have a Sako 75 AND a Sako 85 with this same problem.....not just one action, but two. A problem that has never arisen, with Sako dovetails, on this site......at least in my limited knowledge.

The barrelled action has not been removed from the stock, for checking. I have to disagree, with my fellow posters, about the action strength. It is quite easy to flex an action, that has ejection and magazine ports, with the action screws.....should there be a bind/misalignment with the stock or action bottom metal. If there is any bind/flex, you need to know it now....not later.

Note that, according to your measurements, the rear "flat" is not only lower, but also at an angle......an angle that would occur if the rear tang screw was allowed to pull the rear receiver ring down too far.

After all of the effort you've put into this project......you really owe it to yourself to at least loosen the rear action screw...........to check.

BTW.....over the years Sako has used internal action shims. Something to keep in mind.

Heck......I can't remember the last rifle I DIDN'T break down. You never know what you might find.

Just my $0.02......

Good Luck

 

[paulsonconstruction]

Try putting a .020" shim under the rear tang to see if that straightens things up. Having three rifles with the same issue is odd. Just guessing, but I think the probability of mis-machined inletting would be higher than a mis-machined action. I'll hold the dollar until the jury is in, but keep that nickel handy. Right now, Kevinig looks to be in the lead as your actual measurements are much smaller than I assumed they were from the pic. Like Kevinig, the first thing I do with a newly acquired rifle is remove the stock & check for proper bedding. The Sako team is at work here, so I'm sure they will get to the bottom of it. Keep us posted!

 

[David_S]

Thanks Kevin and Paulsonconstruction. I will be away from the internet for a couple of days so may not be able to post, but will remove the stocks as soon as I return.

Just to clarify. I have 3 Finnlights - two 85s, one in 260Rem and the other in 270WSM, and a 75 in 270WSM.

Both 85s are new and both show the same problem but the 260 is the worse. They have different actions "S" for the 260 and "SM" for the 270. Both have factory set triggers. The stock on the 270 may have been removed by a professional gunsmith when he threaded the barrel for a muzzle brake and both stocks may have been removed at some stage to fit the set triggers. I ordered set triggers with the rifles and Beretta may have swapped them out of another rifle. Just guessing as the set trigger is rather rare.

The 75 was second hand and I do not know if it has the same problem as I have never removed the stock or the scope but I did have a muzzle brake fitted. I don't want to fiddle with the 75 as I need one working rifle.

Poster 22-250 seems to have had the same problem with his 85 so the problem may be not uncommon.

Must go

David

 

[sako-a-series]

David S-Did those silver one pice opti locks come with your rifle? I don't believe I've seen them for sale, just the blued, thanksDave

 

[David_S]

David S-Did those silver one pice opti locks come with your rifle? I don't believe I've seen them for sale, just the blued, thanksDave

No, I bought them from Reloaders Supplies here in New Zealand. They come blued or stainless. I tend to use stainless as I want all-weather rifles (and they look cool with the silver Zeiss scopes!) Website is https://www.reloaders.co.nz/index.php?route=product/category&path=39_52_267&page=2

David

 

[David_S]

Well, Team Sako, I have done some more thinking and measuring.

1) Stock removal

With the help of my son I carefully remeasured the difference in level between a) the front dovetail and the front of the rear dovetail 0.009" and b) between the front dovetail and the rear dovetail immediately in front of the pin recess 0.016"

We then removed the stock from the receiver/barrel and remeasured - no change in measurement. Pictures below.

Next we placed a .020" thick shim under the rear tang as Paulsonconstruction suggested, refitted the stock and tightened the action screws - no change.

There was no sign of the action contacting the stock other than at the tang and the recoil area. To be quite accurate there was a faint indication of contact on one side of the receiver above the magazine. Pictures of the stock below.

Conclusion - the action is not being stressed by the bedding/action screws.

2) Re-examination of Ring/dovetail contact area

We then had a close look at the contact between the rings and the dovetails. First we realised that the rings do not sit on top of the dovetail - there is at least a 0.015" gap - but are held in the groove by the ring clamps and effectively sit on the bottom of the groove, at least we could not insert a 0.0015" (1.5 thou) feeler gauge between the clamp and the groove bottom except on the rear right indicating this rear base is very slightly canted to the left.

We carefully measured the alignment of the bottom of the front dovetail grove with the rear. Effectively there was a 0.010" drop between the front and rear grooves but, unlike the top of the rear dovetail, the front and rear grooves appeared parallel. The rings are mounted 126mm (4.96") apart so this drop equates to the scope being angled upwards by 7MOA.

It also appears that the teeth of the ring clamps are not a good match with the groove as when you tighten the clamp it rotates slightly (see photo below). This is apparent also on both my 20WSMs (75 and 85 Finnlights) which likewise use the one-piece Optilocks.

Conclusion - The problem is caused largely by the difference in height between the rear and front dovetail grooves. It is not helped by the clamp teeth not matching the groove.

3) Comments

Unfortunately this difference is in the "wrong" direction causing the rifle to shoot low and using up valuable scope adjustment to bring on line. Whilst for most hunting ranges (up to 200yds) this may not be a problem it becomes one with longer ranges especially for scopes with ballistic turrets where you compensate for drop by making vertical click adjustments. With my Swarovski 4-12x50 BTW mounted on the 260 all the available vertical adjustment was taken up sighting in at 200 yds rendering the ballistic turret useless, not to mention the inadvisability of operating a scope at the limit of its adjustment.

As I said before, I like the Optilock one-piece rings, particularly because of the polymer inserts. But it would be nice if they had some means of compensating for vertical misalignment such as the eccentric inserts of the similar Burris Signature rings. Or at least if the rifle dovetail grooves were level or the rear one even slightly higher.

So far the Sako 85 Finnlight in 260 Rem appears to be a very accurate rifle. Although we have not yet finalised the load we have had no difficulty shooting sub MOA and have managed several 3-shot groups at 200yds under 1/2" though we are not sure how stable the load is in different conditions. It is a nice light compact rifle ideal for the bush and mountains around here. So we are keen to get out there shooting and hunting (see pictures in the trophy section) not messing around at home with mounts and scopes or discussing warranty issues with Beretta! And I want to get my Sako 85 Finnlight 270WSM sorted too - my son seems to be appropriating the 260 as "his" go-to rifle.

So I think I will "stick" with my "epoxy fix" unless anyone comes up with a better idea. Still interested in and appreciative of Team Sako's comments/suggestions of course.

David
(Edited July 2017 to restore lost Photobucket pictures)

 

[topgear]

Hi David

If it where me I'd file the front ringmount down - bottom and groove to fit. You can do this by hand or if you have a mate with a mill get them to do it. You'd be surprised how easy this is to do. In the days of image moving reticles (Kahles and pecars) it was common to do this. Particularly on the pecar reticle moving scopes with a flat top post to get the horizontal reticle in the centre of the scope. If you modify the front ringmount you should be good to go.

Would be interesting to hear from others with 85's if their rifles are the same. That's quiet a bit of difference.

Cheers John

 

[David_S]

Thanks, Topgear, for the suggestion. I did consider modifying the front ringmount base, but there is not a lot of metal there so I went with the epoxy which seems to be doing the job. The epoxy is really just a filler - when all clamped up it can't go anywhere so strength is not that important.

I have now done both my 85s that way, and if no problems show up with use I will do the 75 if it needs it, as I now have the grinding tool. As I said earlier, I have not touched the 75 up to now as I wanted at least one working Finnlight on hand, but it is probably time I checked how far the reticles are from the centre of the adjustment range at my 200yd sighting-in distance. Will be interesting to see the 75 has the same problem as my 85s.

David

Edit: Just checked the scope and rings on my 75 Finnlight 270WSM. No problems. At 200 yard zero the scope is 12 clicks below the centre position which is pretty much where I want it. So it looks as if the problem might be with 85s only?

 

[NO85CL]

85 Classic with similar problem

I bought a new Sako 85 Finnlight in 260 Rem a few months ago and temporarily fitted an old Leupold Scope in new Sako Ringmounts whilst I awaited delivery of a Swarovski. I noticed I that I had to make considerable vertical scope adjustment to get the shots on paper at 25yards but was not overly concerned as it was only a temporary arrangement whilst I worked up a load. With the right load the rifle proved very accurate and took its first deer a couple of days ago.

I eventually received the Swarovski a couple of weeks ago and bore sighted it with the crosshairs set at the centre of the scope adjustment range. The crosshairs were approximately 6" high at 25 yards. i.e. 24" high at 100 yds corresponding to 96 clicks on the scope! The Swarovski only has a total vertical adjustment of 172 clicks (86 either side of centre) so there was no way I could mount the scope with the crosshairs anywhere near the recommended centre of range. In fact I could not mount it at all without running out of adjustment.

Now the tapered dovetails on the 85 allow windage adjustment but there is no provision that I can see for vertical adjustment, and no easy way of shimming the Ringmounts. (I had opted for Ringmounts rather than the two-piece base types which can be shimmed easily as they were lighter and cheaper, and this is a lightweight mountain rifle).

The underlying problem is that the rear dovetail is not aligned, or even closely aligned, with the front one as can be seen from this photo.



Is this a common problem with the 85s? It is certainly not an isolated instance as I also have a new Sako 85 Finnlight in 270WSM which has the same problem but not as pronounced. Now how can Sako produce a quality rifle / dovetail / ringmount system which won't mount quality scopes such as Swarovski, Zeiss or Leupold? It has somewhat shaken my confidence in Sako quality assurance.

I have, in fact, found a way to shim the Ringmounts on both rifles so that at my 200 yard zero the crosshairs are a little below mid-range, as I want. For the sake of others with similar problems I will post the details when I have a moment.

Has anyone else had this problem? And what did you do? Or am I missing something obvious?

David

Hi David,

Similar problem here, and this is how I fixed it.
I recently took pride ownership of an 85 Classic .30-06, with a Zeiss HT (2,5-10*50) scope. Also used the Optilock ring mounts. The rifle came with the Zeiss mounted. It did not work well. Had to adjust 50 cm or more to the right at 100 mtrs and used up all my ASV+ stops upwards, to compensate for low shooting (so what would I use it for long distance?). It looked like a bad mounting job to me. After some frustration at the range, I went back to the shop. And they fixed it. But even though the mounting looked a bit nicer, I still needed all the compensation. More frustration at the range. Then I read your problem and started to do my own thinking during the night.
The mounting on the rear base is fixed in a way. With the pin, the position is given. But with these Optiloc rings, there is some room for positioning the forward ring on the base. I found out that when you tighten the torx screw that keeps the ring on the base, it actually pulls the ring to the right. I thought that the design had taken that into account, but it does not seem to be that way. Fixing that same screw also pulls the ring somewhat upwards. Now I took the ring apart and moved the lower part of the ring as far forward as I could (with the screw completely loose) on the forward base. This locks the ring in place before you tighten the screw. And guess what. I got all my stops back, both horizontal and vertical alignment (for now based on through bore sighting, but quite reliable).
I have not seen the details of the other base types, but they seem bigger and more robust, with probably less slack?
Here is a picture of the forward ring on the base, after my adjustments. Before changing this, the backside of the forward ring was aligned with the backside of the forward base, right where the chamber starts. There, the base is smaller (due to the slight V-shape), which gives room for error. Again I first thought that the ring was designed to be pulled in place when tightening the screw, but I now think it is not.

Now, the ZEISS is long enough to do it like this on my 'medium' 30.06 chamber, but I guess you should be OK with a Zwarovski too?
You clearly focussed on the back base, but maybe the problem is up front?
I would very much like to know where you have your forward ring!


Hope this is something you have not tried yet

 

[NO85CL]

Well, Team Sako, I have done some more thinking and measuring.

1) Stock removal

We then had a close look at the contact between the rings and the dovetails. First we realised that the rings do not sit on top of the dovetail - there is at least a 0.015" gap - but are held in the groove by the ring clamps and effectively sit on the bottom of the groove, at least we could not insert a 0.0015" (1.5 thou) feeler gauge between the clamp and the groove bottom except on the rear right indicating this rear base is very slightly canted to the left.

Hi David,
Refering to my other reply, this is exactly what I think happens when tightening the clamp in a position on the base where it does not sit stuck without a screw (that is: there is room sideways!) See if you can move the rings on the base to a spot where they actually cannot move when you tighten the clamps. I found that spot on the forward base, which holds the forward ring better down, i.e. lower, which effectively raises the back . I left the back ring as it was. It was enough for MANY stops on my rifle.