What Causes Scopes To Not Hold Zero?

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coleman1495

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I have run into a few instances in which a scope wouldn’t hold zero. It seems to be a fairly common issue.What physically happens inside a scope when they don’t hold zero?
 
It could also be the rings or bases. Double check that everything is mounted securely and torqued properly.
 
Most often this is a quality control issue from assembly. Missing parts, or improperly assembled parts. Over adjusting turrets will often cause problems as well. Less expensive (Chinese, Philippine, Thai, assembeled,) optics would generally be more susceptible to quality control issues.
 
How is it not holding zero? So many variables.

What shooting position configuration?
What gun?
What mounting option and procedure for assembly?
What ammo?
What shooting sequence?
What optics?
Etc etc.
 
ron hilchey said:
Most often this is a quality control issue from assembly. Missing parts, or improperly assembled parts. Over adjusting turrets will often cause problems as well. Less expensive (Chinese, Philippine, Thai, assembeled,) optics would generally be more susceptible to quality control issues.
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Yes this is what I am talking about. Does anyone knows specifically what is going on in the scope typically when it the zero wanders. It seems to be a fairly common issue so I am curious. Any optics experts here?
 
It can be a bit of mystery but I assume loose or detached parts but I don't know which parts
I went 20 years without any scope problems and then had 3 crap out me in 3 years.
One was a budget bushnell that went thru hell and back being mounted to my racoon hunting rifle that spent most of it's life rattling around under the seat of a truck. It did pretty well considering.
The next one I don't even remember the brand...nothing I heard of previous to purchasing the rifle it was mounted on. It then spent 10 years on a 308 before giving it up....during a moose hunt of course.
The next was a 2 year old leupold but they fixed it right up.
 
I have had $2K+ Elcan "not hold zero" on me, only later to find out it was a slightly out of spec pic rail that caused the hold to be not 100% solid all the time. It might be the optics, it might be not. Depending on the answers to the questions I mentioned earlier, beyond those questions if you post some pictures of your targets and the shooting distance it will also help to diagnose. Until then, third party opinions are basically speculation and jumping to conclusion.

In my experience, the more common sighting problem with cheaper (entry level Bushnell, Weaver, etc) scopes is that the adjustments are not precise to the stated spec (e.g. 1/4 MOA at 100 yard etc), and also not very tactile/audible clicks. Less common but possible, is actual wandering zero. Now I have not used "really really cheap" scopes much, so who knows.
 
No idea what is "most common cause", but think of a scope as a "tube within a tube". If the outside tube is solidly attached to the rifle action - i.e. nothing is moving shot to shot, then it is likely the inner tube is not coming back to same place after each shot. Most scope designs I've seen have a single leaf spring about 7:30, pushing back against the vertical (12:00) and horizontal (3:00) adjusting screws. Especially if the spring is weak or rough, it may not get that inner tube exactly back to battery every time. Since crosshairs are in the inner tube, the point of aim is different every time. Could also have loose or worn gimbals at the mounted end of the inner tube. "Wandering zero" can be caused by incorrect attachment of barrel to receiver, barrel shoulder not perfectly square to line of bore, inconsistent contact between fore arm and barrel, or the action itself shifting under recoil in the stock. I have a frankenparts 6.5x55 Swede mauser that will walk 140 grain Sierra's across a 100 yard target about 10 inches over 20 shots. Haven't found the specific issue yet, but see above for the most likely culprits.
 
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My experience is also that the most common issue is the failure of the spring.
In some sense that is to be expected at some time because this things cannot hold up forever.

It's just a matter of how well it is made and how good the parts are.
Good scope you expect to last for years with heavy use (or abuse).

I had a Zeiss fail after 3 years. They did replace a spring for free.
Most good scopes I had lasted for many years.
 
norlandgeese said:
I have had $2K+ Elcan "not hold zero" on me, only later to find out it was a slightly out of spec pic rail that caused the hold to be not 100% solid all the time. It might be the optics, it might be not. Depending on the answers to the questions I mentioned earlier, beyond those questions if you post some pictures of your targets and the shooting distance it will also help to diagnose. Until then, third party opinions are basically speculation and jumping to conclusion.

In my experience, the more common sighting problem with cheaper (entry level Bushnell, Weaver, etc) scopes is that the adjustments are not precise to the stated spec (e.g. 1/4 MOA at 100 yard etc), and also not very tactile/audible clicks. Less common but possible, is actual wandering zero. Now I have not used "really really cheap" scopes much, so who knows.
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I am not asking for help troubleshooting a specific set up. I am asking why/how scopes can have wandering zero.
 
Potashminer said:
No idea what is "most common cause", but think of a scope as a "tube within a tube". If the outside tube is solidly attached to the rifle action - i.e. nothing is moving shot to shot, then it is likely the inner tube is not coming back to same place after each shot. Most scope designs I've seen have a single leaf spring about 7:30, pushing back against the vertical (12:00) and horizontal (3:00) adjusting screws. Especially if the spring is weak or rough, it may not get that inner tube exactly back to battery every time. Since crosshairs are in the inner tube, the point of aim is different every time. Could also have loose or worn gimbals at the mounted end of the inner tube. "Wandering zero" can be caused by incorrect attachment of barrel to receiver, barrel shoulder not perfectly square to line of bore, inconsistent contact between fore arm and barrel, or the action itself shifting under recoil in the stock. I have a frankenparts 6.5x55 Swede mauser that will walk 140 grain Sierra's across a 100 yard target about 10 inches over 20 shots. Haven't found the specific issue yet, but see above for the most likely culprits.
Click to expand...

This makes sense. Gives me an idea of what would be going on. Thanks for the explanation.
 
A member at my club was complaining about his red dot not staying at zero....

It ended up being a red dot that was ment for airsoft...lol. it couldnt take the recoil of a SW sport AR

To answer your questions. There could be a few reasons. One of the major issues...its just a cheap red dot/ scope or not mounted correctly. Everything seems like a tight fit until t a few rounds thru a rifle and the recoil loosens the locking attachment.
 
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sunjeep24 said:
A member at my club was complaining about his red dot not staying at zero....

It ended up being a red dot that was ment for airsoft...lol. it couldnt take the recoil of a SW sport AR

To answer your questions. There could be a few reasons. One of the major issues...its just a cheap red dot/ scope or not mounted correctly. Everything seems like a tight fit until t a few rounds thru a rifle and the recoil loosens the locking attachment.
Click to expand...

I am not sure how to be more clear about this. I am talking about scopes that do not hold zero. I realize there are other reasons for shifting zero but that’s not what I am talking about. I know how to mount and troubleshoot a scope. I am wondering about the specific issues with the internals of the scope.
 
Thanks for clarifying, this is the kind of info you’re after perhaps....

Tactical Scopes: Mechanical Performance Part 2
http://precisionrifleblog.com/2014/08/22/tactical-scopes-mechanical-performance-part-2/

Tactical Scopes: Mechanical Performance Part 1
http://precisionrifleblog.com/2014/08/13/tactical-scopes-mechanical-performance-part-1/

how-a-rifle-scope-works1.png
 
Spring failure or fatigue, mis-aligned rings/base that bend the tube, ring too close to rear of adjustment knobs can affect the inner tube movement, sticky adjustment, long list of things that can go south.
 
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