What am I doing wrong. Have moved scope back and forth. Can torque the back ring no problem to 25. As soon as the front ring starts to get snug the parallax binds up ??
Rifle Scopes Spuhr binds parallax ?????
- Thread starter deersniper
- Start date
Yes. The parallax binds up as soon as you get the front 6 screws finger tight. 12 or 15 does the same thing
About to do feeler gauges but the objective and turret housing aren’t touching. It’s tight but you can see main tube on both sides
Does same thing mounted backwards with just the rear ring somewhat tight aslo
Threw it in a NF magmount. Torqued to 25. 0 issues.
Threw it in a NF magmount. Torqued to 25. 0 issues.
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I don’t know if it matters but are the half clamps in their proper spot forward and aft?
Edit never mind saw them in the picture
Edit never mind saw them in the picture
Had the same issue when I had an erector housing (Spuhr w/ S&B) so close to cap. It even looked like yours, where it appeared to have space...but as soon as I moved scope back 1/4", parallax knob was normal.
Acknowledged from above...not an option for this setup.
Acknowledged from above...not an option for this setup.
Asking
So far I’m 0/2 with Spuhr.
I think the scope gods are punishing me for straying from NF scopes and rings
hows that my answer lol. I bought this stupid Spuhr so I could run a clip on on the a700 clip on rail.
So far I’m 0/2 with Spuhr.
I think the scope gods are punishing me for straying from NF scopes and rings
^yes. Thanks for that. But when the front ring is at 12 the parallax binds.
If I tighten just the very front 2 screws out of 6 I don’t have problems. I would almost run it that way if I didn’t want to put a heavy rangefinder on top.
If I tighten just the very front 2 screws out of 6 I don’t have problems. I would almost run it that way if I didn’t want to put a heavy rangefinder on top.
Do you have any other 34mm rings laying around to try? Have you tried torquing the spuhr mount with it detached from the rail?
Worked fine in a NF unimount. I will try torquing it bare and see if anything looks whacked in there
Sorry - missed your earlier reference to the NF unimount. Sounds like Spuhr is the issue.
I ran a spuhr on a k318i for a good while. It takes some playing but off the top of my head, I think I was right at 10 or 12 inch lbs on the front, never had an issue running either of my simrads up there on it. Hell, it may have only been around 8 inch lbs. I know I couldn't go across the screws again after hitting torque on them all or it would bind. I think I did the center ones top and bottom then ran the front and rears in together. Not sure at the moment. There's not much room up there on those optics to spread the load across the mechanical internals. They're not the only ones that have this issue.
Had the same issue with a Spuhr and Tangent Theta. Finger tight on the front cap would cause the parallax knob to bind. Never had an issue with Spuhrs and Vortex Razors, though.
Thanks. If I can’t figure it out i guess I will put my atacr on the DT and move the 318 to the AI
How’s that scope been for you? I took this one on trade never really looked at them before that
Might be time to swap to ARC M10 rings...
This seems to be a pattern across many brands of optics with spuhr mounts from time to time.
I have either experienced or known people who have had an issues with everything from razors to thetas.
I have either experienced or known people who have had an issues with everything from razors to thetas.
I'm curious and talking outloud.
Could you use Plastigage to give you a measurement of the caps.
I wonder if there is a variation in the caps or a radial flex happening from torquing.
Anyway,I'd bet Mile high or Spuhr would know more than me.
Could you use Plastigage to give you a measurement of the caps.
I wonder if there is a variation in the caps or a radial flex happening from torquing.
Anyway,I'd bet Mile high or Spuhr would know more than me.
Just get the 35mm version of the Spuhr and a good layer of epoxy around the scope tube.
Job jobbed.
Job jobbed.
Not sure how to do all that. I turned the scope around and using just the rear cap does the same thing
To be clear I took the scope out turned it around and tightened the ring cap closest to the objective and it caused the same problems
I have a hypothesis, I have no data to support this other than other sensitive machine parts I have designed and dealt with that were sensitive to this.
I mention this because I see others here stating they have seen similar issues on other scopes so I almost want to take the Spuhr out of the equation and look elsewhere. I wonder if something is inducing a moment into the center housing.
I have no experience with a Nightforce Unimount but It appears that they have a much narrower clamp seat and cap compared to the wider seat and cap in the Spuhr providing more distance between the seats. Assuming the Spuhr seats are concentric the next thing to consider is the concentricity of the scope tubes. It is possible that the tubes on the scope are not perfectly, or near perfectly, concentric. Since the wide seats on the Spuhr are less forgiving to concentricity because the distance between the seats is less and the width of the seat is great enough to force the scope tube to be concentric on the adjacent seat. Any significant deviation in the concentricity of the tubes will induce a moment into the center housing when the second clamp is tightened. I am surprised that it is happening when the screws are finger tight.
If you had access to a Coordinate Measuring Machine (CMM) you could check the concentricity of both the Spuhr and the scope tubes.
All that said, if, and that's a big if, that is the problem, I don’t know how to resolve it easily.
I mention this because I see others here stating they have seen similar issues on other scopes so I almost want to take the Spuhr out of the equation and look elsewhere. I wonder if something is inducing a moment into the center housing.
I have no experience with a Nightforce Unimount but It appears that they have a much narrower clamp seat and cap compared to the wider seat and cap in the Spuhr providing more distance between the seats. Assuming the Spuhr seats are concentric the next thing to consider is the concentricity of the scope tubes. It is possible that the tubes on the scope are not perfectly, or near perfectly, concentric. Since the wide seats on the Spuhr are less forgiving to concentricity because the distance between the seats is less and the width of the seat is great enough to force the scope tube to be concentric on the adjacent seat. Any significant deviation in the concentricity of the tubes will induce a moment into the center housing when the second clamp is tightened. I am surprised that it is happening when the screws are finger tight.
If you had access to a Coordinate Measuring Machine (CMM) you could check the concentricity of both the Spuhr and the scope tubes.
All that said, if, and that's a big if, that is the problem, I don’t know how to resolve it easily.
You’re not alone. FDE 4002 caused mine to bind up. I Fed with it a lot with zero percent success. Same mount also left significant marks on my 4-16 ATACR at 18”/lbs. Seems to have survived that. I tried another Spuhr and there was no issues but I was sour and now Era-Tac and won’t look back. (Have a Badger COMM too but that doesn’t rhyme.)
Sorry if I missed it but does it do the same thing if you torque the opposite cap and then finger tight the other? This "may" confirm a concentricity issue.
Whenever you tighten the objective ring it’s problems.
Ocular ring tight AF. Good to go.
This will sound like a complete juvenile question but your sure the scope isn’t contacting the base? Mag ring etc. stupid question I know but can’t see how it would do that unless the mount is really that far off
Edit: this would be in reference to causing the tube to slightly bend when tightening
Edit: this would be in reference to causing the tube to slightly bend when tightening
I think you’re on the right track. The spuhr rings are so long, it leaves very little room for tolerances.
Agreed. I am thinking that because there is so little room for tolerance stack up, any concentricity issues are going to be amplified. It would be interesting to measure these components on a CMM and know for sure.
@deersniper I potentially had the same issue with my Kahles K318i in a Geissele Super Precision Mount and 45 degree RMR mount so it’s not just your Spuhr mount. I torqued screws down to scope specs and parallax would not adjust. I backed off the torque and made sure scope was not moving by hand. I then took it out to shoot everything zeroed and maintained zero so I have not messed with it since. The next thing I was going to do was blue loctite screws in mount but after several shoots it’s fine. I posted some pics with my Burris and did Not experience this parallax effect with the Burris XTR3 3-18x50. That said the Burris had a bit more room from the turret housing. The Kahles turret housing is large and apparently in charge lol. FYI mount and optic is on my AI AT. I’ll post some of my Kahles in the same mount once back at work if that helps. I also had to move the RMR mount to the rear ring base as the front did not clear the Kahles scope bell.
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This happens sometimes. I've had it happen with several brands of scope. Likely the tube that carries the parallax adjusting lens set I'd beyond it's toleranced maximum material condition.
I have a degree in engineering, and like to dabble in optics. I've spent more money than I'd like to admit on things, just to take apart and experiment with. The last was a milsurp Raytheon made M1 Abrams beamsplitter day/night gunsight. I'm not an optical engineer like Koshkin, but as this issue is related to the scopes mechanicals, I feel qualified to weigh in.
In my opinion, the most likely cause is a little tolerance stacking between the inside diameter of the outer tube, and the outside diameter of the moveable tube that carries the lense set that moves to adjust parallax.
The terms used to describe the extreme limits in tolerancing parts are "maximum material condition" and "least material condition.
Maximum material condition occurs when a part has had the least amount of material removed (contains the maximum volume of material), and is still dimensionally in-spec. For example, if a tube is supposed to be bored to a diameter of 1 inch, and is toleranced to +.004" to -0.00", then any part with an internal diameter from 1.00" up to 1.004" is acceptable. That part is said to be in maximum material condition when the internal diameter is 1.00". (Here, the smaller hole is considered MMC because that results in the part having more material).
Least material condition is the opposite. For example, that same part would be in least material condition when it has an internal diameter of 1.004". In both cases the part would be acceptable.
The opposite is true when it's the outside diameter that's referenced. For example, if the OD of tube is spec'd to be 1.00 inch, +.002" to -.002", it would be in LMC @ 0.998" and in MMC @ 1.02". In both cases, the part would be acceptable.
So, if the OD of the parallax adjusting tube inside the scope missed QC, and made it into the scope while being a a few ten thousandths beyond MMC, and at the same time the ID of the main tube happened to be on the MMC side of its tolerancing, it would take very little compression of the outer tube from the mount to cause binding.
The reverse is also true. If the internal diameter of the outer tube was the part that made it past QC and is beyond it's allowable MMC (bored a couple ten thousandths too small), and the inner telescoping tube was within spec, but on the MMC side of its tolerance, binding could occur under when the mount is tightened and the metal compresses a little.
Of course, other factors, as mentioned in a previous post, (even if within spec), such as alignment of the front/rear tube sections (parallelism), out-of-round, etc, would magnify the effects on the one out of tolerance part.
It doesn't happen frequently with high quality products, but it does happen. All it takes is one slightly out of spec part, and a little bad luck. A slightly oversized (beyond MMC) inner tube may fit fine in a middle of spec outer tube, but as luck would have it, sometimes it gets paired with a within spec but MMC outer tube.
Consider returning the scope to the manufacturer for inspection and/or repair
I have a degree in engineering, and like to dabble in optics. I've spent more money than I'd like to admit on things, just to take apart and experiment with. The last was a milsurp Raytheon made M1 Abrams beamsplitter day/night gunsight. I'm not an optical engineer like Koshkin, but as this issue is related to the scopes mechanicals, I feel qualified to weigh in.
In my opinion, the most likely cause is a little tolerance stacking between the inside diameter of the outer tube, and the outside diameter of the moveable tube that carries the lense set that moves to adjust parallax.
The terms used to describe the extreme limits in tolerancing parts are "maximum material condition" and "least material condition.
Maximum material condition occurs when a part has had the least amount of material removed (contains the maximum volume of material), and is still dimensionally in-spec. For example, if a tube is supposed to be bored to a diameter of 1 inch, and is toleranced to +.004" to -0.00", then any part with an internal diameter from 1.00" up to 1.004" is acceptable. That part is said to be in maximum material condition when the internal diameter is 1.00". (Here, the smaller hole is considered MMC because that results in the part having more material).
Least material condition is the opposite. For example, that same part would be in least material condition when it has an internal diameter of 1.004". In both cases the part would be acceptable.
The opposite is true when it's the outside diameter that's referenced. For example, if the OD of tube is spec'd to be 1.00 inch, +.002" to -.002", it would be in LMC @ 0.998" and in MMC @ 1.02". In both cases, the part would be acceptable.
So, if the OD of the parallax adjusting tube inside the scope missed QC, and made it into the scope while being a a few ten thousandths beyond MMC, and at the same time the ID of the main tube happened to be on the MMC side of its tolerancing, it would take very little compression of the outer tube from the mount to cause binding.
The reverse is also true. If the internal diameter of the outer tube was the part that made it past QC and is beyond it's allowable MMC (bored a couple ten thousandths too small), and the inner telescoping tube was within spec, but on the MMC side of its tolerance, binding could occur under when the mount is tightened and the metal compresses a little.
Of course, other factors, as mentioned in a previous post, (even if within spec), such as alignment of the front/rear tube sections (parallelism), out-of-round, etc, would magnify the effects on the one out of tolerance part.
It doesn't happen frequently with high quality products, but it does happen. All it takes is one slightly out of spec part, and a little bad luck. A slightly oversized (beyond MMC) inner tube may fit fine in a middle of spec outer tube, but as luck would have it, sometimes it gets paired with a within spec but MMC outer tube.
Consider returning the scope to the manufacturer for inspection and/or repair
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It's a good scope. Definitely a stubby little thing. I had it about 18 months and it was my first Kahles. I ended up moving it down the line because I wanted to go back to a 25x optic, I wanted to try out the T3 reticle and I absolutely hated the top mounted parallax. I ended up grabbing a MK5HD as a cheaper way to try out T3 and planned to get a TT in T3 if I decided to stay with the reticle and keep the MK5HD on a secondary rifle for backup. I like the MK5HD so much I doubt I'll drop the coin on a TT at this point. The kahles had a tough ass finish on it and that little thing took a beating on my AX, before that it was on a TL3 build and in between those two it was on a LMT MRP. I used it a good bit with my simrads too.
Cool thanks. Now I don’t feel bad about downgrading in durability on the AI going from NF to something else
I'm not an ATACR fan, so I'll just say that I don't think the kahles will give you any durability issues.
The issue is that it typically only happens with one brand of mount. And several brands of high end optics.
I have spoken to many of the manufacturers and it’s a common theme. As soon as you swap the rings/mount, the issue goes away.
What we may have is a mount that due to its dimensions, doesn’t always allow for what would be considered acceptable tolerances by an optics manufacturer.
So, I think it’s definitely not as simple as a mechanical defect on the optics side.
Yes, I can also see how that Spuhr, which has more surface area applying force to the tube than most other brands, could cause issues. If a portion of that large surface area were tightened around a part of the tube with close toleranced moving parts inside.
In cases where two mating tubes end up on the MMC side of their respective tolerance range, they are less tolerant of external clamping forces. In other cases, when the tubes end up closer to the middle of the tolerances, the same mount works fine.
The area just forward of the turret housing seemed to be the culprit in the Vortex and IOR scopes I saw with this issue. When the front ring was moved further forward the problem went away. Close tolerances are a double edged sword.
Unfortunately, deersniper has no room left on his scope. But, a set of rings that allow him to clear that area just forward of the turret housing may work fine.
Considering the Nightforce mount that worked fine has significantly wider spacing, and less clamp area, that supports this idea.
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I have serious doubts that the front and rear main tube sections on any modern scope are so non-concentric that it would cause issues with 1-piece mounts. If that were the case, then NF, MPA, Era-Tac, ARC, etc mounts would all have issues. Instead, you hear of one mount (Spuhr) having issues with a long list of different optic manufacturers.
I don't know how the Spuhrs are made, if the two holes are machined as one with a long tool, or if they are EDM'd? Maybe it's as simple as the wide Spuhr clamping force being too close to the turrets, specifically the parallax mechanism.
When I had my issues with a TT, there were a couple people that reached out to me with the same issue, but I chalked it up to a thin tube on the scope even though many other people didn't have any issues with the TT+Spuhr combo. Now hearing more about all the other scopes having the same issue, I'm wondering what it is about the Spuhr that's causing it.
I don't know how the Spuhrs are made, if the two holes are machined as one with a long tool, or if they are EDM'd? Maybe it's as simple as the wide Spuhr clamping force being too close to the turrets, specifically the parallax mechanism.
When I had my issues with a TT, there were a couple people that reached out to me with the same issue, but I chalked it up to a thin tube on the scope even though many other people didn't have any issues with the TT+Spuhr combo. Now hearing more about all the other scopes having the same issue, I'm wondering what it is about the Spuhr that's causing it.
I don't doubt that Spuhr machines their holes strait and concentric. I agree with you, that the combination of the Spuhrs large clamping area, and perhaps thinner scope tubes are contributing factors.
I'm not sure what the size/pitch of the screws Spuhr uses, but for the sake of argument I'll guess it's 8-36 or similar.
I looked up the tightening torque/clamping force for 8-36 screws in one of my old textbooks. It says that 20 inch lbs of torque on a 8-36 screw results in 600lbs of clamping force from that screw.
With 6 screws per cap, that results in the cap putting 3600lbs of clamping force on the tube. If that cap happens to be wrapped around a tube, with another closely toleranced tube inside it, I can see how it would bind.
If the same 8-36 screw has lube or locktight on the threads, it becomes 15 in lb per 600 lbs of clamping force per screw.
Are people mounting scopes so close to the housing using other mounts? Maybe the larger mount is forcing it, or at a minimum making it more likely to happen... highlighting the Spuhr.
Would not the large surface area of the Spuhr spread the compression force over a larger area of the maintube and thereby not compress the maintube as much as a narrower ring?
I think this a scope problem and not a Spuhr problem. I think if you clamped the maintube near the turret with a NF ring, the parallax would bind. It just so happens the NF ringmount spaces the rings so far apart that they don’t affect the parallax mechanism
I think this a scope problem and not a Spuhr problem. I think if you clamped the maintube near the turret with a NF ring, the parallax would bind. It just so happens the NF ringmount spaces the rings so far apart that they don’t affect the parallax mechanism
Several manufacturers have been trying to repeat the issue with other rings and as far as they have told me, have only been able to recreate it with the spuhr.
Manufacturers might have a tendency to ‘test’ things with a desired outcome in mind.
Seems pretty easy for us to grab x brand mount and install y brand scope with housing pushed up against it....and applying some of Ken’s numbers, tighten it down with same overall force as directed by 25”lb Spuhr caps.
Bottom line, I find it hard to believe Spuhr has the market cornered on squeezing parallax parts.
Seems pretty easy for us to grab x brand mount and install y brand scope with housing pushed up against it....and applying some of Ken’s numbers, tighten it down with same overall force as directed by 25”lb Spuhr caps.
Bottom line, I find it hard to believe Spuhr has the market cornered on squeezing parallax parts.
I've had this happen using Seekins, Warne and a few other brands of rings, and on several scope brands.
In all of those cases, I resolved the issue by moving the rings further away from the turret housing.
Your right in that more area = less pressure (pressure=force divided by area). But more area gives you less options for location.
There are a few brands of scope that have this issue damn near every time I've had a ring near the turret housing, and a couple brands that seem to be fine, regardless of which mount is used or what spacing.
In all of those cases, I resolved the issue by moving the rings further away from the turret housing.
Your right in that more area = less pressure (pressure=force divided by area). But more area gives you less options for location.
There are a few brands of scope that have this issue damn near every time I've had a ring near the turret housing, and a couple brands that seem to be fine, regardless of which mount is used or what spacing.
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