30MOA base + 28" barrel = reduced image quality?

Discussion in 'Long Range Hunting & Shooting' started by 6.5x300, Jan 31, 2014.

  1. 6.5x300

    6.5x300 Well-Known Member

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    Has there been any discussion on the potential of the end of the barrel hindering the view/image quality at high magnification when mounted on a 30 MOA base?

    Here is my set up.....

    28" stainless 1" bull barrel (no taper)
    30MOA Ferrel one piece base
    Savage 110 long action
    Burris XTR low 30mm rings
    8-32x56 Sightron SIII MOA-2 scope (70 MOA of elv travel)

    Everything came together and looks perfect. I got about 1/8" of clearance between the barrel and the objective bell yet I am certain at magnifications above 20x I am getting reduced image quality do to the barrel being in the field of view. Looking at the side view of the rifle with the scope set at 30MOA I am nearly certain the end of the barrel is in the way of the field of view of the scope.

    I obviously know how to fix the problem....... less MOA in the base, higher rings, shorter barrel, maybe paint the barrel black??????

    Has anyone else experienced this problem with long barrels and high angle MOA scope bases?

    Thanks

    BT
     
  2. azsugarbear

    azsugarbear Well-Known Member

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    Many of us have experienced something similar when we mounted our optics close to a barrel that also had fixed front sites on it. At high power, the outline/blurr of the front site blade was visible, but rarely got in the way of the overall site picture. At low power, it was still there, but the optical illusion made it all but disappear.

    So in a nutshell, you're not alone. Obviously, a barrel muzzle is much larger than a front site so the distraction would be more pronounced. You have already outlined the most common fixes for it.
     
  3. Canadian Bushman

    Canadian Bushman Well-Known Member

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    I would tolerate it as long as it didnt interfere with my shooting, or go with higher rings. Just my opinion.
     
  4. WildRose

    WildRose Well-Known Member

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    I've had similar problems before with scoping a rifle that has a front sight. Having such a blurr in the scope drives me nuts and causes eye fatigue if you spend much time looking through it.

    What caliber is this on? Why do you need 30moa?

    If it were me and I needed that much then I'd use taller rings but that too can cause issues with trying to get a good mount every time.
     
  5. 6.5x300

    6.5x300 Well-Known Member

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    300wm

    Ferrel was out of the 20 moa bases at the time I ordered. It was either 10 MOA or 30. I don't necessary need 30 MOA base. Everything else I have is 20 MOA bases and haven't had any issues. I had the elv travel in the scope for a 30 MOA base and figured.... why not! But now...... seems like a waste of a good scope giving up image clarity like this.
     
  6. westcliffe01

    westcliffe01 Well-Known Member

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    Something odd about this situation... 30 min is only half a degree. Scope to barrel c/line should be about 1.5" if not more. The vertical displacement of the optical centerline over 28" is only a 1/4". So if we start with a c/line distance of 1.5" then deduct half the barrel diameter we are at 1" then deduct the 1/4" from the tilt we are at 3/4" from edge of the muzzle to c/line of optical image. Working backwards, 3/4 over 28" is an angle of 1.534 deg.

    Looking at the scope specs, at min magnification the FOV is 12.2ft at 100 yards. The half angle of that is 1.165 deg. Since 1.165 is less than 1.534 deg, it means that the barrel should be out of the field of view at Min magnification. Obviously, as the magnification increases, the FOV reduces, which should take the muzzle further and further from the FOV.

    So here is what I think. I don't think you have line of sight to the muzzle itself. I think the barrel is reflecting incident light into the ocular and that is what you are seeing. Given that this is a scope with a very narrow field of view, you should get a substantial improvement from using a lens shade. Worst case scenario, you may need to do something to cut reflection from the barrel. You might initially try a strip of black electrical tape on the top of the barrel on the full length. If this substantially improves the image, then the best thing you can do is figure a way to blacken the barrel. But a long lens shade should substantially improve the image and cutting reflection off the barrel would be the ultimate to solve this issue.
     
  7. varmintH8R

    varmintH8R Well-Known Member

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    I am not familiar with Sightrons, but have had other scopes where image quality is dimmer at high mag. I'm not sure if you have tried it or not, but you may want to unmount it, set it on a sandbag, and test it like a spotting scope.

    If if still looks dim, call Sightron.

    If it looks clear, I agree that taping the barrel to reduce glare is the cheapest and easiest first step.

    Let us know when (and how) you solve it.

    Good luck

    Brandon
     
  8. WildRose

    WildRose Well-Known Member

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    Images will always be dimmer at higher magnification. You only have a given amount of light to work with so the more you magnify it the dimmer the resolved image will be.

    The problem is worse with cheaper scopes due to reduced light transmission but all else being equal it just take more light to give an equally bright resolution when you increase magnification.

    That's why when doing microscopy you can only go so far using a reflector and ambient light and then you have to use a dedicated light source when you get to higher magnification.
     
  9. westcliffe01

    westcliffe01 Well-Known Member

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    This sounds like a glare / stray light issue. It is a high magnification scope and image clarity will suffer greatly from stray light. A low magnification scope is made to have a wide field of view, and so cannot be shielded in the same way from glare, but at the same time has a huge exit pupil and so would not be degraded in the same way.

    The black tape test should provide answers for the OP.

     
  10. 6.5x300

    6.5x300 Well-Known Member

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    Yep I need to unmounts the scope from the gun and check it.

    I did the numbers too with the angle being only .5 of a degree. I modeled it all up in AutoCAD. I'll have to check the numbers again and study a bit more on the subject. Probably just what you guys said.... Glare from the shiny SS barrel.

    If I modeled it up correctly and basically drew a straight line from the lower edge of the scope forward on the same 30 MOA plane the line intersects the barrel about 9" back from the end of the barrel.

    I'll experiment a bit more but do appreciate the input and welcome further thoughts.

    Thanks

    BT
     
  11. Canadian Bushman

    Canadian Bushman Well-Known Member

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    Check with the scope dialed all the way out. If it is a small problem now it may be a larger problem when you dial another 60 moa elevation.
     
  12. westcliffe01

    westcliffe01 Well-Known Member

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    The field of view is on the scope specification 12.2ft at 100 yards at 8x. Half of that is on 1 side of the optical centerline. You can't use the outer edge of the lens or ocular, thats not how it works. FOV is an angle from the C/L of the scope.

    [​IMG]
    This is from the Sightron website. The dimension B (center to lowest tick mark) is 60moa at 8x power and the angle we are talking about is 1.169x 60 min = 69.9 MOA. Its not hard to recognize that 70MOA is going to take you to the edge of the field of view when dimension B is 60 MOA already.

    At 32x dim B = 20MOA

    This is a high quality scope. I'm sure it is the barrel reflection / glare.

     
  13. WildRose

    WildRose Well-Known Member

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    Being an old carpenter at heart let me make a suggestion. Advertised specs are one thing but if you want a quick answer you can see let me suggest this.

    Remove the scope and rings.

    Lay a straight edge such as a yard stick running the length of the rail.

    Slide it forward till it either contacts the barrel or runs past the end of it.

    Another simple test would be to put the sunshade on it while it's still mounted and see if that makes a difference.

    Taking it out at night and just sighting on a target in the headlights will also give you a quick answer.

    If it's glare off of the barrel that will not be an issue at night using only headlights provided you are behind the light source.
     
  14. westcliffe01

    westcliffe01 Well-Known Member

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    Final comment: Since mounting the scope, did you dial the elevation turret DOWN 30MOA to get a basic zero on the scope ? If not, you will be 30 MOA closer to the barrel than reflected by the previous calculations.

    The scope only has 70MOA of windage and elevation so you will only have 5moa to work with to zero the scope after dialing in 30min to correct for the rail tilt. Based on that, a 30 Min rail was probably not a good idea for this scope. It may be necessary to shim the front end of the rail to get the scope to zero.