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Shiming scope ring/tube.

Ray BRay B Member Posts: 11,822
edited September 2015 in Ask the Experts
I have a scope mount that was intended for a 26mm scope, but it appears the ring is actually 26.5mm. With the ring tightened completely together the scope tube has no play but is not tight, under recoil (7x57) the scope drifts forward and changes the "zero". I've tried "stoning" down the mating surfaces as much as I dare and the tube still slides. I've put a coat of fingernail polish inside the ring but the tube still drifts.

Does anyone know of a tape, possibly on the line of plumbers Teflon that could be used between the tube and ring to buildup the tolerance but unlike Teflon would have friction?

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    MobuckMobuck Member Posts: 13,860 ✭✭✭✭
    edited November -1
    If you don't want to replace the rings, you might get by using weather proof double stick tape like is used to attach emblems and trim to vehicles. I'd put it on the top half if I were doing it.
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    waltermoewaltermoe Member Posts: 2,073 ✭✭✭✭
    edited November -1
    If your using a one inch scope tube and the rings are 26.5 mm, you would have I believe 35.5 thousands of an inch gap. you stoned the faces down on the rings you said, that would take up some of the gap on top and bottom, but you will still have a gap on the sides, that is probably why the scope is drifting. You could maybe try and use some brass shim stock that is at least 15 thousands, or go to the old stand by fix all tape, Duck Tape, some duct tapes run 15 thousand thick.
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    Ray BRay B Member Posts: 11,822
    edited November -1
    The scope is a 26mm tube Kollmorgen. the rings are part of a side mount unit so are not changeable unless I have the ring and bridge drilled (the action is a 1916 Mauser) so that isn't going to happen. the problem appears to be .5mm. It is tighter since I stoned the faces, but still moves. the recoil isn't significant since I'm shooting 150 bullets in a 7x57. So it shouldn't take a whole lot to hold the scope in place.

    As noted I tried fingernail polish. the most recent attempt is with Gorilla Glue. It has dried and the excess has been peeled off. I haven't been to the range to test this fix yet. but if it slips, I'll look into either the brass sheeting or the head gasket sealer, or both.
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    KAMsalesKAMsales Member Posts: 1,672 ✭✭✭✭✭
    edited November -1
    You need to trim and epoxy in some .010" shim stock on the top and bottom halves of the scope ring. The other option would be to get a 26.5mm to 1" ring adapter and have a machinist ream it to 26mm
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    nononsensenononsense Member Posts: 10,928 ✭✭✭✭
    edited November -1
    Ray B,

    In order to correct a poster above:

    1 mm = 0.03937" (that's pretty close to 40 thousandths...)

    1/2 of that is 0.019685" or pretty close to 20 thousandths.

    1/2 of that in order to shim both top and bottom is 0.010" or 10 thousandths approximately.

    I would machine a reducer but that's because I can.

    In your position, you have created an oblate or a slight oblong by stoning the mating surfaces. So there will be more pressure on the top and bottom of the scope tube now. In order to provide some cushioning effect, I would resort to the gasket material or rubber cement since the shim stock is standard thickness and not tapered.

    We use this process when securing large diameter, long barrels in barrel blocks for unlimited benchrest rifles.

    Best.
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    5mmgunguy5mmgunguy Member Posts: 3,853
    edited November -1
    As already noted I would use some .010 shim stock. Cut it to fit the ring width with a length to fit the circumference. Clean all surfaces
    and assemble. Plan two send nononsense a note asking him if you could pay him to machine a reducer.
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    pip5255pip5255 Member Posts: 1,631 ✭✭✭
    edited November -1
    remove all existing glues and start over, take 4 thin O rings that are the size to fit the outer tube(like 1"), cut them in halves, place 2 halves in each ring bottom side by side, set scope in place,make all adjustments, set other halves on top of tube, set ring tops in place and tighten. should hold firmly and not mar any surfaces, even works ok with one O ring.
    just because you could doesn't mean you should
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    dfletcherdfletcher Member Posts: 8,164 ✭✭✭
    edited November -1
    I have an old Jaeger sidemount on a Winchester 43 Deluxe in 218 Bee that uses a scope with a larger than 1" diamter tube. I use a 1" tube steel Weaver. Even more challenging, the rings are not split but made of a material that has some bend to it. I used brass sheeting strips cut to fit. It was easy to work with and bends with the rings when (if) I ever need to change out the scope.

    Why can't anything be easy ......[;)]
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