Ideal scope height?

Discussion in 'Gunsmithing' started by lazylabs, Oct 16, 2007.

  1. lazylabs

    lazylabs Well-Known Member

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    Does anyone have a good number for the height from the top of the cheek piece on the stock to the center point of the scope? Lets assume there are no clearance problems with the scope objective. I am working on a bull pup style stock and trying to decide on base height. Thanks
     
  2. HeskethPritchard

    HeskethPritchard Well-Known Member

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    Surely you should just get the scope as low as possible?

    This is of course driven by the bell housing diameter (driven by the type of scope you want/need for the work your gonna do) that ultimately drives the height you want to know.
     

  3. lazylabs

    lazylabs Well-Known Member

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    Since I am mounting the scope foward of the action which is 1.600 and the barrel is only 1.350 I could actually mount he scope so low that they eye piece would be very low on the action. It also places your face over the widest part of the gun, your head would be at quite an angle to get centered. I will probably offset the scope base to be left of center on the rifle to help with that I am just not sure how high. Thanks
     
  4. LouBoyd

    LouBoyd Well-Known Member

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    There are good reasons not to mount a scope as low as possible. The reasons I can see for keeping a scope as low as possible above the bore include minimizing the torque on the rings when the gun is fired, making the scope less likely (maybe) to get caught on brush while being carried, and perhaps to keep the shooters head as low as possible on a battle rifle.

    The main concern as to how high a scope should be mountd in my opinion is that the scopes optical axis should be comfortable for the shooter. Either too low or too high will be uncomfortable and won't give a proper "cheek weld" . If "tight to the barrel" is the most comfortable position maybe the rifle's stock needs a higher comb. Obviously the shape of the stock's comb relative to the bore matters. So does the relative shape of the shooter's face, neck, and shoulders, so there's no "right" answer to the exact distance a scope should be mounted from the barrel. On certain classes of firearms a scope needs to be mounted beside the barrel, not above it. An example is a shoulder fired recoilless rifle, or grenade launchers like the M70 and M203.

    Reasons for raising the scope include the fact that if a rifle is set up to maximize the "point blank" range such that from zero out to some maximum distance a bullet will fall in a given diameter circle if the sights are aimed at the center of the circle, then the scope height above the bore should be equal to the radius of that circle. That could be rediculous if a very large or very small point blank error diameter is desired but it makes sense for a 5 or six inch diameter circle.

    Mounting a scope high also puts the bore lower relative to the shoulder, and assuming the stock is designed for it, reducing the rotational recoil moment when a gun is fired. That helps reduce muzzle flip. The AR-15 is an example of a rifle designed with this and the previous reason in mind. The M14 and M1 were not.

    Another reason to keep the scope high is that thermal distortion from warm air rising off a heated barrel is more likely to miss being in the line of sight the higher the scope is mounted if there is any crosswind.

    There is a slight increase in sensitivity to canting by mounting a scope higher. On the other hand it's easier to notice that a rifle is canted with the scope mounted higher.
     
    Last edited: Oct 21, 2007
  5. devildoc

    devildoc Well-Known Member

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    As Lou touched on, there are two ways to tackle the issue. You can either fit the comb to the sight height, or fit the sight height to the comb. Both are limited, either by the clearance between the objective and the barrel or the starting dimensions of the stock and the selection of base/ring heights. I'd start by having the person who the rifle is being fitted to mount the unscoped rifle and measure the distance between his line of sight and the top of where you plan on mounting the scope. then figure from there how high you want to mount the scope and how much comb to shave off.
     
  6. Ridge Runner

    Ridge Runner Well-Known Member

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    does it really matter as long as the scope is perfectly in line with the bore L&R?
    here's my thoughts, a flat top AR-15 typicaly has the scope 3.5" above the center of bore just due to the design of the rifle.
    Now that 3.5" amounts to 17" of useable trajectory at 500 yds, ya know thats 17" of drop ya don't even hafta wory with.
    RR
     
  7. bagul

    bagul New Member

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    I don't get what you are trying to make. a gun with a 1.35" barrel is meant to be shot at short ranges and would not need a scope...or maybe i missed something?
     
  8. lazylabs

    lazylabs Well-Known Member

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    The "comb" will be the action of the gun so it's not adjustable. The scope will be mounted above the barrel on a block not on top of the action. When I refered to 1.350 that's barrel diameter. I am just going to use a removable scope base on the barrel block so I will have the option of changing heights.
     
  9. wildcat

    wildcat Well-Known Member

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    Lazylabs, what are you building and could you give us the specs.

    Wildcat
     
  10. lazylabs

    lazylabs Well-Known Member

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    It will be a bullpup style gun with a lawton 8000 action and chambered in something based on the 408 case and probably necked to 375 but possibly 338, either AM or snipe-tac. I am working on the barrel block and stock design now. I was going to mill the scope base into the block but may go with a bolt on scope base for flexability. I don't really want to use and adjustable cheek piece. I will probably end up offsetting the scope to the left of the centerline of the barrel to make it a little more comfortable. I got the idea from the pics Dave Wilson posted on here of his 338 edge bullpup. If I go with 375 with a shorter barrel and bullpup design it might be sorta managable for hunting.