Box Test - what does this mean?

Discussion in 'Long Range Scopes and Other Optics' started by tlk, Nov 9, 2011.

  1. tlk

    tlk Well-Known Member

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    Box test this last weekend. I have repeated this test a couple of times and get the same results. I would expect the groups to remain the same but they are not. What do you make of this?

    boxtest1.jpg

    1st group is my zeroed group is 0.233" (probably cannot see the details), and includes my return to zero shot. I am not counting the cb shot for this test.

    2nd group is low right - 0.572".

    3rd group is high left - 0.443"

    4th group is low left - 0.793"

    5th group is high right - 0.258"


    Is there something wrong with the scope or me? How can I dial through all of these shots and not get but one group that is consistent with my zero?

    Thanks for your help.
     
  2. Scot E

    Scot E Well-Known Member

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    I have no idea how experienced you are at this so if some of these concepts or questions are elementary I apologize up front.

    it is a bit hard to read your target. How for away was the target for the box test?

    Any wind issues you were dealing with?

    What scope?

    Did you change power magnification during the test?

    I assume you and your gun can consistently shoot groups similar to the center one?

    There are a lot of different ways to do box tests and a lot pitfalls that you can run into that you have to work through to figure out the real problems. I know a couple guys that simply can't shoot as tight of groups once they start box testing scopes. It is weird but I think it is a mental thing. They know where the center group should go based on their shooting but they start dialing and they loose that confidence I guess and their groups open up a bit every time. I can shoot that gun and get the same groups all around. So first make sure you are executing those box test shots the EXACT same way you do the center shots.

    Do you know how close to optical center you are on your scope? Your upper groups are close to the same as center but your lower groups are both lower. If you are beginning to reach the max of your turrets you will not get the same kind of repeatable distance per click.

    Did your zero return once you finished the test? I personally wouldn't be too concerned about group size yet. The slightest change in conditions, shooting form, gun rest, etc can make some pretty serious changes.
     
  3. LouBoyd

    LouBoyd Well-Known Member

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    The thing which would disturb me about that target are that the two lower groups are noticeably lower on the target than they should be. I assume you calculated the number of moa/click to determine how many clicks to use. Certainly the vertical clicks in your scope are larger in angle then the horizontal clicks, which they should not be, and the lower horizontal clicks are larger than the upper horizontal clicks, though not by as much.

    With only 3 shot groups it's hard to tell if those deviations are real or just small number statistics. Some scopes do become "loose" when used near the limits of their movement range, usually on the side where the springs are most extended. Also, a box test will be more sensitive to rifle canting in the corners than in the center, though I don't see evidence in the target that's happening. It does appear that the scope is returning to zero properly,

    In your other test targets was the lower left group always largest and the upper right always best? Was the difference in the size of the click equally noticeable?
    If so I think that's significant and points to a problem with the scope. That's why box tests need to be done.

    There's a lot you didn't say in your post:
    What range to the target
    How large (in MOA, clicks, and inches on the target) are the sides of the box.
    What make and model scope.
    What rings and base
    What rifle
    What cartridge and bullet
    What shooting style (benchrest, bags, prone, etc)
     
  4. tlk

    tlk Well-Known Member

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    Scot, thanks for the reply. No insults taken here, just want to get it all straightened out. Here are the answers to your questions:

    I was at 100 yards prone. No wind. Scope is a super sniper fixed 10, so no power changes. There were no changes for focus or parallax over the testing period. Other specs: 30-06, 168 smk, 56.5 gr h4350, cci primer, lapua brass. Bullets were all consistent in bearing surface length andeach powder charge was weighed on a calibrated beam scale. Rifle is a Mauser action with a 28" heavy sporting contour barrel. Ring are Burris xtr and bases are weaver. Shots were taken prone. Target sides were 4" from center (you can see this in the pic I think).

    I can get a group consistently under .35" if prone. I finally found a load specs the rifle likes (lots of reading and using info off of this site). What gives (to me) evidence that something is up is that I dialed low right (.572"), high left (.443"), low left (.793"), high right (.258") and back to zero (.233") - it seems to be consistent. I initially thought it was me as well, but it is consistent across multiple tests, including the zero grouping around a quarter inch (btw, never got a group that tight until I applied the methods listed out in the parallax thread).

    The scope is close to center, about 2 moa low and right iirc.
     
    Last edited: Nov 9, 2011
  5. Scot E

    Scot E Well-Known Member

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    Well, it seems like you are doing everything right. Assuming you dialed correctly, I think that scope is mil dot reticle but MOA turret right?, The 2 bottom targets are off too far. I would say something is wrong.

    A couple things you can do.

    1. Shoot a ladder test, not the load development style but shoot straight up and straight over every 1 or 2 MOA for 10-20 MOA (whatever you have room to do on your target). See if you get consistent results. Then dial down and across, 1 or 2 moa for both turrets, and see if you find any irregularities. I would also be curious to see if you shot another test but only moved up from your zero. Those top targets seem to be pretty good but the bottom ones are not. Make an aim point on that target so you can shoot maybe 4moa up and 8moa up or maybe 8 and 12 moa up. You could also go further down past 4 moa and see if things straighten out or if they stay the same or get worse.

    One thing to check. A lot of times scopes get tightened way too tight and if you have crappy rings, or poor QC, you can get a pretty bad pinch going on at the tube and that pressure will affect the way the erector moves inside the tube. I have fixed a couple just like this. On one I could actually feel the turret bind just a bit when I hit a certain spot. When the rings were loosened this went away and the reticle moved as it should. An option to check at least.

    Leupold makes a magnetic boresighter that is really helpful in diagnosing issues like this. Once you square it to your muzzle and reticle you can watch the reticle move as you dial the turret and make sure it is matching up with the measurements on the boresighter. This device is invaluable for all kinds of scope checks. It can't diagnose everything, some tings are caused from recoil related issues but it will do a lot. It is fantastic for this kind of thing as well as verifying turret repeatability, accuracy and also reticle subtention accuracy.

    I hate little issues like this! Good luck on your search!

    Scot E.
     
  6. Gene

    Gene Well-Known Member

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    The purpose of a box test is to check your scope for its tracking. Groups are not necessary. Before you start, your scope and rifle should be aligned properly so that reticule is not canted. Start by laying a small 1" bubble level on any flat surface, such as rifle action. At the same time, use a 6" or so 90 degree level to line up the butt plate. Your rifle should be laying in a solid rest to do this. Both bubbles should agree. Now go to the range and set rifle on a solid front and rear rest. If you can, have someone adjust in any direction while you hold rifle steady and watch movement of the reticule. Move reticule one minute at a time around the target corners at 100 yds.

    BOX TEST:
    I take a 2' level to the range to make sure the target is not canted. Then I hang a 2' string attached to a plum bob nearby. The vertical crosshairs should line up with the string. If not, loosen scope and rotate until it is. Take a few practice shots at 100 yds., and adjust scope to hit dead center. Start at upper left corner of a 1" square target; adjust scope 1 minute to right, fire a shot; adjust one minue down, fire one shot, and so on. Your fifth shot should be very close to the first shot, if you have an accurate rifle. Repeat this test on a second target. The five shots might be off the corners by a hair, depending on how accurate the rifle is. If shots are off more than 1/2" or so, you have a tracking problem.
     
  7. tlk

    tlk Well-Known Member

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    OK, here is the original target that called out the issue. No top of the box, only lower (it was so "off" that I wanted to re check my gear). Note that there are two shots high from center as I was sighting the scope back in, they are not part of the tracking test.

    box test 2.jpg

    What is different about this test is that I shot twice each in order: center, low right, low left. I then dialed through the triangle again for a single shot at each, just to make sure there was an issue. Seems to return to zero fine.

    Center group: 0.274"
    Low right group: 0.786"
    Low left group: 0.641"

    Gene, to your point I made sure in both tests that my target was level (used a level) and the rifle was as well. Scope and rifle are aligned properly. I will do the tests suggested this weekend.

    OK, maybe I am dense, but even if it isn't tracking, it still shouldn't open the groups up like that. The only time I have seen that is when something is loose in the scope; had it happen once - every time the firing pin hit the crosshairs would jump to a new place. But the center group confirms that this isn't taking place. It is a mystery to me. Do any of you know the reason for this?


    Thanks for help. Greatly appreciated.
     
  8. Gene

    Gene Well-Known Member

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    Yes, the internal components of your scope could cause the problem. There could be erector tube or spring movements. What scope do you have? Target adjustments? By all means, try another scope before you evaluate condition of this one.
     
  9. Scot E

    Scot E Well-Known Member

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    Erector issues could cause the groups to open up as well as the tracking issues.