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Out of adjustment, is my scope broke?

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Chris Farris View Drop Down

Joined: October/01/2003
Location: Texas
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chris Farris Quote  Post ReplyReply Direct Link To This Post Topic: Out of adjustment, is my scope broke?
    Posted: April/11/2007 at 14:49

One of the most common problems we hear about concerning scopes is that the scope has run out of adjustment and will not sight in.  If this happens to you it does not mean that the scope is broken (99% of the time), it just means that the scope ran out of adjustment.  The problem lies with what required the scope to use so much adjustment.


The most common culprit is the mounting hardware (base and or rings).  Poor quality rings and bases or improperly installed rings and bases can cause the scope to be so severely misaligned with the bore that the scope does not have enough internal adjustment to compensate.


There are several techniques that can help you determine if it’s the rings or bases.  If you are using "Weaver" style rings and you run out of adjustments left or right make a note as to the location on the target where you ran out, then remount the rings 180 degrees from the way they were mounted originally.  Sight it in again, and if you run out of adjustments the opposite direction you initially did, then it’s the rings.  Usually when this happens it is possible to turn one of the rings back around and get the gun sighted in.  This is a band-aid fix and not recommended as a method to solve the problem.


If you are using "Redfield" style rings and you run out of adjustment left or right it is most likely because the rear rings is not centered on the base.  If it is centered try the same technique used for "Weaver" style rings mentioned above.


If reversing both rings and single rings in different combinations does not yield any different results it is most likely not the rings.  Next you will need to diagnose the base.   Some one piece and most two piece bases can be reversed, try this first.  If the different combinations do not reveal an issue it is most likely not the base.  If you can not reverse the base(s), try using a different base from either the same manufacturer or preferably a different manufacturer.  Many times we run into a bad lot of bases so switching brands is most effective.

If the problem is with the rings or bases you can sometimes solve the problem by lapping the rings, shimming the base and or rings or use Burris Signature rings, which have interchangeable plastic inserts that act as shims.  The best solution would be to replace the poor quality mounts with quality mounts that require no shimming.


The second most common culprit is the firearm its self having the mounting holes drilled off center.  This is very difficult in most cases to detect without some precise measuring equipment.  In gross cases you can simply “connect the dots” and extend the lines beyond the receiver and see the problem.  Not very common years ago but becoming more common today.


The third most common culprit is the scope but it is not running out of adjustment that is the problem.  It’s the adjustments getting stuck, not responding to external adjustment or simply jumping all over the place.  You can very easily diagnose the scope by first centering the reticle then visually watch the crosshairs move by using a boresighter.  Look up the scope’s specs and see if it moves the stated amount in each direction.  Keep in mind that a scope with 40 inches of travel means that it goes 20 inches in any direction from optical center.   If it does not move at all something has happened with the gear assembly, if it moves but not the entire adjustment range then something is causing it to bind (bent tube or rings over tightened).  If it is jumping all over the place the reticle retention spring is defective.


Replacing the scope that ran out of adjustments with a different scope that was able to be sighted-in is not a valid method to determine if the first scope is defective because different scopes have different internal adjustment ranges.  The higher the magnification the less internal adjustment a scope will have and additionally different manufacturers use different size internal lenses which will cause them to have more or less internal adjustment.  IE: A Schmidt Bender 3-12 will have substantially less internal travel than a Swarovski 3-12 as would a Leupold 3-9 vs. a Leupold 8.5-25.


The rarest culprit is also related to the firearm its s

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cheaptrick View Drop Down

Joined: September/27/2004
Location: South Carolina
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cheaptrick Quote  Post ReplyReply Direct Link To This Post Posted: May/15/2007 at 12:10
Excellent thread, Chris.
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pyro6999 View Drop Down
Optics Retard
Optics Retard

Joined: December/22/2006
Location: North Dakota
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pyro6999 Quote  Post ReplyReply Direct Link To This Post Posted: May/15/2007 at 21:53

thats some great stuff to read thanks chris!!

They call me "Boots"
375H&H Mag: Yeah, it kills stuff "extra dead"

343 we will never forget

God Bless Chris Ledoux
"good ride cowboy"
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Clark View Drop Down
Optics Apprentice
Optics Apprentice

Joined: February/13/2004
Location: Near Seattle
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Points: 121
Post Options Post Options   Thanks (0) Thanks(0)   Quote Clark Quote  Post ReplyReply Direct Link To This Post Posted: May/20/2007 at 11:30
I agree with Chris in principal, but not the 99%.
He just sees good scopes.

I have over a dozen Leupold scopes, and some are 40 years old.
Every last one of them will bore sight to the same spot if in the middle of the elevation and windage  adjustment range.
So that bounds the Leupolds between 92 and 100%.
And if there were a problem, Leupold would fix or replace it.
Old Weavers and no name old Asian scopes are probably at 90%.
I have at least a dozen scopes in my scope junk yard that are unusable.

But 90% of the time, even with crummy old scopes, it is usually something other than the scope.

Over the last 8 years I have been involved in sporterizing ~60 Mauser rifles.

At gun shows I sometimes buy failed Mauser sporterizing projects, just to get the parts for cheap.

All of the failures seem to be that the scope or peep sight would not sight in.

The problems I see:
1) miss match of rings at different heights
2) drill and tap off center
3) charging hump interferes with rear mount
4) Different Mausers, different heights, one pair of bases does not fit all

By that last one, what I mean is that if I 1-2-3 block up a Mauser receiver on a surface table and measure the difference between the height the front and rear scope mounts must mate with, there is a variation in Mausers.

These are 98 Mausers and per the chart would take Weaver #45 and Weaver #46 mounts:
1903 Turk .123"
K98 .151"
VZ24 .165"
1938 Turk .171"
Santa Barbra commercial .159"

The difference in thickness between mounts:
1) The Farrell single piece mount  is .157".
2)  Steel Warner Weaver style:  .166"
3) Weaver #46 #45:  .173"

I have many 1903 Turks made in Oberndorf.
.173" - .123" = .050" error
I can calculate the impact these difference cause
[change at target] / [3600" =100y to target] = [mount height change] / [
5" between mounts]
change at target = .050" 3600"/ 5" = 36"

Actually it is not quite that bad, as the barrel threads have some cant with respect to the receiver bottom.
But the remedy is as follows:
Shim the front mount until a scope [in the middle of it's elevation adjustment range ] will bore sight.

I used to have to work with a benchrest  on lawn furniture the deck  and bore sight to the top of a telephone pole during the daylight hours.
But now that SWFA sold me this Leupold magnetic bore sighter for $60, I can sit on the sofa and bore sight at midnight, which is what I was doing last night at midnight:)
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