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"broken" scopes...

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Unread 03-26-2006, 07:22 AM
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Join Date: Feb 2005
Posts: 563
\"broken\" scopes...

A reprise of a piece I wrote for my webpage a year or so back. Seems apropo here again. [img]/ubbthreads/images/graemlins/wink.gif[/img]

I once spoke to a Leupold tech via telephone and he confided to me that fully 2/3's of the scopes that are returned to Leupold for "repair" really aren't broken at all. I asked if Leupold informed the scope's owners that their scopes weren't broken, and he said "rarely." It would seem that if folks go to all of the trouble of sending in a scope which they believe is broken, they want something done. Telling customers that there is nothing wrong with their scopes gives them a "1-2" punch, so to speak; they don't get anything done to their scope, and they are also made to look inept for having sent in a fully functional scope for repair. So Leupold generally just gives the scope a good going over, charts the erector movement, and returns the scope.

But what would cause someone to think that a scope had "failed" when in truth it really hadn't?

The most common reason for scope sighting problems which isn't related to the scope itself would be, of course, a mounting problem.

If you mount a scope on a base which isn't aligned closely to the barrel's bore (that's bore, not necessarily barrel, since some bores aren't drilled straight through the barrel) you may have a hard time zeroing the scope at particular ranges.

If the base is slanted up or down, as opposed to being parallel with the bore, you'll need to dial in quite a bit of elevation correction to get on target. Normally, this won't be much of a problem unless you run out of "come ups" for that 600 yard target you're trying to hit.

Or, if the scope base is off to the left/right with relation to the bore, you'll need to dial in quite a bit of windage to get zeroed. Here's what can then happen:

(Sorry about the blurry images... just imagine this particular "scope" is a BSA). [img]/ubbthreads/images/graemlins/laugh.gif[/img]

Look at the top image. The green circle represents the erector inside the scope tube. In the top image, the erector is relatively centered, with plenty of room to move up/down/right/left. This is how you hope your erector will align when you zero your rifle.

In the second image down, the erector has been dialed over to one side. This may be to compensate for a base/ring system that isn't in line with the rifle's bore. While you can zero the scope for closer ranges, you won't be able to dial the elevation up to reach longer ranges because, as you can see in the diagram, the erector will hit the inside of the scope tube at about 2 o'clock (or 4 o'clock if it is moving down). This scenario is what is often the case when the scope will zero just fine at 100 to 200 yards, but the shooter runs into trouble when he tries to get a 300 yard or farther zero. A scope which fails a BOX TEST may merely be a victim of a bad mount, and in fact have no internal problems at all. Further, if you find that your windage zero drifts off to the left or right as you dial in elevation, you may be forcing the erector to follow the curve of the inside of the tube (slightly), thereby forcing it aside.

In the third image in the stack, you will see an example of a "dialed up" erector; it's at its upward limit of movement. If you were to try to dial in 15 MOA of windage at this high elevation setting you might get half of that. Then the erector would hit the inside of the scope tube and stop. The shooter might say "Damn. This scope works great except when I try to dial windage at 1000 yards. I'm gonna send it back to Burris." (or Leupold or USO or whomever).

The larger scope tubes don't really have any advantage at all as far as light transmission--but they have a significant advantage when it comes to internal adjustment room. A 30mm scope tube could be mounted on a "crooked" base and ring set and still dial right in, and likely work fine as far as "come ups" too. Therefore, one might replace a 1" tube scope with a 30mm scope and find that a tracking problem has gone away. The 1" scope will be blamed, but a faulty mount may be the true culprit.

Scope which are mounted with their tubes in a bind can do all kinds of funny things. Erector zoom changes in zero, and crooked or inconsistent tracking come to mind.

In many cases, when we replace what we believe is a broken scope, we also change out the mounting rings. By installing a good set of rings which are better aligned, the new scope is able to function as it is supposed to--but the old scope would have too, had it been properly mounted.

The point of this whole piece is to get folks to understand that in many (perhaps most) cases where a well made scope seems to be having problems, it really may not be a scope issue at all; it may in fact be a mounting issue.

I know, I know... <"I lapped them thar rings and mounted that thar scope perfek! Cuz ats the way I do all of muh scopes. Thank you vary much~!">


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Unread 03-26-2006, 09:09 AM
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Join Date: Dec 2005
Posts: 2,483
Re: \"broken\" scopes...

Green788, your comment: "A scope which fails a BOX TEST may merely be a victim of a bad mount, and in fact have no internal problems at all." interests me. Is that the one where shooting groups at the corners of an imaginary 'box' on paper is used to test a scope?

Your comments about scopes being returned and nothing's wrong with them got my attention. I talked with John Unertl many years ago about such things and he said words to the tune of: "Most folks don't shoot well enough to tell a good scope from a bad one. Especially if they shoot a 'box' test."
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Unread 03-26-2006, 09:40 AM
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Join Date: Jan 2002
Posts: 439
Re: \"broken\" scopes...

Green, good post. This is the reason why I used only good quality one piece base. There is less chance of misalignment. Brand new scope usually come out of the factory with erector tube relatively in the center, at least Leupold is. When mounting a new scope or even a used scope, I make sure that the erector is centered and then I'll confirmed this with the collimator. Before I touch that dial, I will get that crosshair in line with the bore as closed as possible. Factory rifle is notorious for misaligned bore. A mismatch ring and base is also one of the culprit of misalignment.
With regards to Leupold service, it is the best in the industry. That's one reason why I'm their customer for life. My hunting buddies and I were rough with our equipment. It's comforting to know that you have a company that backs their product 100% no question asked.
To achieve the maximum possible accuracy, all variables must be remove or at least minimize.
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Unread 03-26-2006, 10:33 AM
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Join Date: Feb 2005
Posts: 563
Re: \"broken\" scopes...

Thanks guys.

Bart, yes, the box test that many folks like to do on a scope when they first mount it goes something like (variations exist, of course)... Dial the scope to zero at 100 yards. Then dial 10 MOA left and fire a group. Then dial 10 MOA up and fire a group, then dial 20 MOA right and fire a group, then 10 MOA down and fire a group, then dial 10 MOA left, which should put you back on your 100 yard zero and fire another couple shots to confirm.

If the scope will be used on a 1000 yard rifle, you would want to increase the vertical size of the box accordingly. This could mean dialing left 10 MOA, then up as high as 40 MOA (to get to a 1000 yard zero). You'd need a BIG target board to do this at 100 yards, of course. [img]/ubbthreads/images/graemlins/smile.gif[/img]

Some scopes will track well enough to make a pretty good "box" shape. None I've ever seen were perfect, but this is likely owning in many cases to the accuracy of the rifle.

You could also simply use a scope collimator to see if the crosshairs point to where you dial them. However, at some extreme adjustment points, the erector won't hold zero well under the recoil of the rifle. So I prefer to actually shoot paper to be sure...

I call my own variation of the box test the "Tall T test." My own feelings are that all you really need to do is start with a 100 yard zero and then dial all the way up to your highest (longest range) zero point. Fire a group there. Then go left 10 MOA, and then right 20 MOA, firing groups at each of those points. You should have a very elongated "T" shape. If the windage is working well at the highest point of erector travel, it should be working just fine at all points below there. This saves time, ammo, and does the same thing as a box test--in my opinion.

I think it's a good idea to run the turrets of a new (or even an old) scope end to end several times before trusting its adjustments. Sometimes grease gets sticky, or there may be machining marks on bearing surfaces which need to be worn down by repeated movement. The erector spring or springs may need some flexing from extreme to extreme before they'll settle in to a predictable pressure pattern.

I think it's very important to run the turrets end to end on a scope at least every six months or so. If you do this regularly--and certainly when the scope is new, you may find that the "sticky erector" gremlin doesn't come to visit you. [img]/ubbthreads/images/graemlins/smile.gif[/img] Lots of scopes seem to need a shot or two to shake the erector to its new zero after you make an adjustment. If you run the turrets in, and keep the grease and the bearing surfaces excercised, repeatability will be much improved, even on cheaper scopes.

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Unread 03-26-2006, 12:24 PM
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Join Date: May 2001
Location: Sask. Canada
Posts: 2,410
Re: \"broken\" scopes...

I have visited the Leupold plant, had a very detailed tour and they told me exactly what you mentioned about most scopes having no real problem. At that time they had one heavy barreled rifle (in 30-06 as I recall) that they would use if they felt shooting was warranted. Probably have other rifle(s) now but the guy told me that old '06 was accurate enough for their needs.

Said they just boxed most of the scopes up and sent them back, just like you said. They get a few duds, I have one that is going back shortly but that happens with most brands.
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Unread 03-27-2006, 06:57 AM
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Join Date: Mar 2004
Location: Germany
Posts: 658
Re: \"broken\" scopes...

Ian, would this be an abt time to offer to sell you a S&B?
thier failure rate is thes than .1% as far as i can remember.
Occupying the British Zone. www.roedaleprecision.com
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