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Mounted Scope bases

countershaftcountershaft Member Posts: 320 ✭✭✭
edited June 2008 in Ask the Experts
How can you tell if the bases (drilled and tapped) on the barrel and action are on correctly ? In line with the bore . I have two scopes that I mount on a rifle that both have to go so far left , they touch the inside of the mount to be on target .

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    RCrosbyRCrosby Member Posts: 3,808 ✭✭✭
    edited November -1
    I'm not sure what kind of mount/ring set up you have, but it sounds like whatever it is, you have to use all of the lateral adjustment to get where you need to be?
    Not sure if this would help, but when mounting a new scope I first determine the total adjustment range available to me; i.e. turn each turret as far as it will go to the right, then count the rotations it takes to get all the way to the extreme left, then return half that distance to the right. This will position the crosshairs at the center of the scope and should give you the best idea of whether your bases are properly aligned. Again it would help to know which mounts you have; whether there are adjustments available to you front and rear? Rear only? etc.
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    countershaftcountershaft Member Posts: 320 ✭✭✭
    edited November -1
    I'm mounting an older type B&L 6 x 24 Balavar varmit scope . With outside cross hair adjustments. I slip the scope mount groves into the bases , bore sight and have to bring( with the screw adjustment) the rear of the scope all the way to the left (Against the inside of the mount) to get it to center in the bull.I have no (to the right) lateral movement left. These mounts are hard to adjust .
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    Guns & GlassGuns & Glass Member Posts: 864 ✭✭✭✭
    edited November -1
    This design uses target style bases. One maybe mounted on the front reciever, and the other on the barrel.

    If base radius, screw hole vertical axis, wrong screw heads, base dimensions, barrel radius are off in any way adjustment will be negatively affected.

    The scope has multiple adjustments: Windage & Elevation are in the external ring, and the Objective. Also depending on the mount (two styles) ther is one in the scope bottom.

    Usually the issues is adjustments are not done correctly.

    Now as to checking the bases, one of the easiest ways is to:
    1. Level the rifle via the bases flat top. Firmly secure.
    2. Lay a stiff square straight edge on the base top of the rear and across the front. Observe any gaps (light)from under the edge.
    3. Lay the straight edge along the base sides. Using the rear as a guide observe the fit on the front base.
    4. Reverse the procedure using the front as reference to double check


    Adding to RCrosy's post it is best to unscrew both W & E till a light stiffness is felt, then follow his instruction. This will provide what I call the Optical Mechanical Centering.
    More often than not the cross hair will not be centered...but it's a good close procedure. Ther is another most correct way but it's more time consuming, and requires some practice.

    As per your subject you posted, if you'll email me..I'll send you FACTORY adjustment instructions. Free.
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    RCrosbyRCrosby Member Posts: 3,808 ✭✭✭
    edited November -1
    Pictures would sure help, but it sounds like we may be talking about two
    different systems. (Maybe not.) The B & L bases I'm familiar with (had a pair on a M.70) mounted in the tradition positions, front and rear of receiver, and basically provide elevation through the forward V-block (which had eccentric discs on left and right) and simply rotated in place, the rear adjustment looked similar but the "V" moved to the left or right as adjustment screws were turned.
    The other system, often seen with forward ring on the barrel and rear on the front of the receiver, holds the scope in place through opposing plungers set into a large diameter "ring".
    Pictures of each, anyone? Sure would help.
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