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shims

Postby PopGun » Sun Jun 21, 2009 11:15 pm

Has anyone ever damaged a scope by using shims to raise it a little?
one would have thought, one would have found a better way to pass the time, in the middle of infinity
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Re: shims

Postby Beer Hunter » Mon Jun 22, 2009 7:59 am

Are you running out of clicks?

Kev.
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Re: shims

Postby Keef » Mon Jun 22, 2009 8:56 am

Do you want to use the shims to raise the whole scope so that the objective front lenses clears the barrel or do you want to tilt the scope so that you have more adjustment?

If you need the clearance then fit higher mounts.

If you want to tilt the scope say on here and I will put on how to do it without shims and without straining the scope.

If you shim it there is a very real risk of damaging the scope with the mounts.
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Re: shims

Postby varminter » Mon Jun 22, 2009 11:40 am

Keef wrote:...If you shim it there is a very real risk of damaging the scope with the mounts.

I hope not! I've just done this - though only as a temporary expedient, with a cheap (sub-£100) scope, where I encountered a mysterious looseness in one ring that I thought was 1" to match the tube but... I partly corrected the difficulty by fitting a ring top-half from another set, and made up the (minimal) slack with bits cut from an old feeler gauge; I can only guess that the dodgy ring is one of the fairly rare examples of a 26mm ring masquerading as 25.4mm....
I tightened the shimmed ring on carefully, to 14lb-ft/ins, using a torque driver I got on Ebay for a bit over £20, excellent bit of kit that's around £80 new, reassuring to use. But I hope the scope doesn't shift or suffer damage in the way you suggest might be possible. But why should it? The shims aren't quite as wide as the ring, but not narrow enough to dig into the scope tube I'd have thought. Have you experienced this?
Regards, Malcolm
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Re: shims

Postby PopGun » Mon Jun 22, 2009 6:30 pm

Beer Hunter wrote:Are you running out of clicks?

Kev.


No Kev, I never had the right mounts and thought I could get away with putting some shims in,
I made them to my own specs and concluded that although they would need changing as I couldn't expect them to hold properly as I was too concerned to tighten down,
they would get me up and shooting, and they did work for a week or so,
then i noticed the shot was edging left, time had come to tighten down or spend money, I went and bought some high mounts for £27,
but alas as I took the medium mounts off I noticed some pinch marks,this being done at the rifle range in front of people, I was very red faced, I managed to discretely hide the damage with the new mounts,but I fear it is only down to luck that I can still use the scope, :oops:
talk about loosing your footing, I have had a nasty reality check, and find myself questioning everything,
its a nauseating experience, I was thinking it might help if I knew someone else had made the same mistake. :worried:
one would have thought, one would have found a better way to pass the time, in the middle of infinity
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Re: shims

Postby Keef » Mon Jun 22, 2009 9:36 pm

Shimming can do some serious damage to the scope if care is not taken.

Imagine a tube on top of two equal height supports. If you raise the height of one of the supports the tube only contacts the edges of the support, in this case the mounts. When you tighten up the top caps pressure is put on the tube pushing it down onto the edge which often results in a dent in the scope tube.

A better alternative is:

centralise the ret in the middle of it's run. Check that it is perfectly central by putting it in some vee cut in a box and aim it at a distant aiming point. Rotate the scope 180 degrees if the ret is not on the aim, halve the error and recheck. do this for the verticle and horizontal.

Mix up some epoxy putty and roll it into a thin strip. Cut two pieces just big enough to line the bottom mountput in place and cover with cling film.

Place the scope in the mount and gently seat it. Put the top caps on and very lightly nip up the screws.

At your chosen range start to zero the scope by firing a few shots. instead of altering the point of impact of the shots for height with the scope adjusters, alter the height of the point of aim by tightening the top caps to compress the epoxy putty. Tighten the front mount to raise the point of impatc, the rear cap to lower it.

Once zeroed for height leave the scope in the mounts for the putty to harden. Take the scope backout and remove the cling film and reassemble the scope and caps.

If you need more clicks for range set the zeroing low when doing this so there is a tilt on the scope. the scope will be fully supported on the mounts without the risk on putting a dent in the tube.
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Re: shims

Postby c18rch » Tue Jun 23, 2009 9:07 am

Useful tip :thup:

I assume you would have to do it to both top and bottom of both rings though. Otherwise there will still be a pressure point where the to rings are pinching. Eg, if raised by your method at the back the back edge of the top half of the rear ring and front rings and the front edge of the of the bottom half of the front ring will cause pinch points. :?

Also I have found that clear silicone shoe polish works really well for releaseing epoxy.

Rich
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Re: shims

Postby Keef » Tue Jun 23, 2009 9:13 am

The mounts are set at 90 degrees to the rifle and the poxy in effect allows the angle to be changed without giving a pinch.

If you use top caps with four screws the caps will follow the angle of the scope without needing epoxy.

I have used wax as a release agent for epoxy when bedding an action. The one I use is supposed to be for lubricating the bed on my planner thicknesser!
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Re: shims

Postby varminter » Tue Jun 23, 2009 9:24 am

Keef wrote:The mounts are set at 90 degrees to the rifle and the poxy in effect allows the angle to be changed without giving a pinch.
...

Great suggestion I hadn't thought of, and I'm an established user of epoxy resins/glues for various applications: building canoes, fishing rods, running repairs... I think my use of shims in this instance is not likely to produce pinch/pressure points, since I have a front ring that is fractionally wider than the rear, so shimming it top & bottom ought to retain self-centering and maintain the same axis established for the scope tube by the rear ring. That's my theory anyway... I might yet have to try your epoxy trick! Idea filed away inside head, hope it can be retrieved when necessary.
Regards, Malcolm
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