Have you ever actually damaged a scope from shimming?

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tibblet

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I'm sitting here grumpily shimming a set of rings that I just bought, and it got me wondering if all the tales from the "don't shim" crowd have any truth to them. I ended up searching for quite a long time to see if I can find any pictures or real-world accounts of someone who has actually "over shimmed" and damaged a tube.
After a long time and many searches, I gave up and even asked ChatGPT if it could find anything for me.... and it couldn't.

So.... has anyone damaged a tube before? How much shimming is really too much? I'm starting to think a lot of the information out there is based on very little practical evidence. Would love to see some pics of actual "over shim damage".
 
I shimmed the front scope mount after dropping and bending an old bushnell scope.
It worked fine untill I replaced it but I used a piece of plastic that was too narrow and it left a dent in the tube.
I didn't really care as it was a cheap scope but would have a shim the width of the scope rings in the future.
It was a "for now" fix. I'd be inclined to just replace what was needed these days.
 
What happens to the inside diameter of the rings when you place a shim inside the rings. The scope tube is one inch, the inside of the rings is one inch... place that 25 thou shim inside the bottom ring ... now you have an inside diameter of .975" and a tube size of 1". That will deform the scope tube, possibly beyond elastic abilities and most likely a dented scope tube and scratched as well from the edges of the shim.

Shims should be between the base and the action.

Think about it... say you want to raise the front of the scope... You are using Leupold rings. So you place a 25 thou shim in the bottom of the front ring and place the scope on top of that... the scope does not fit but you now place the top half on the ring on the scope. (It fits over the tube). Tighten the rings screws and force the scope into the bottom of the ring. The ring and shim are not going to compress, the scope tube is going to compress and distort. Usually this permanently damages the scope tube.
 
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I would imagine the worst thing you can do is shim unevenly, not all the way around the scope. Because then you have an uneven clamping surface, and have an eccentric clamping load on what is essentially a thin metal straw. Worst case, you have two point loads, one at either end of the shim and an eccentric load across the upper half of the surface of the scope, but at an angle, since the scope tube is now not in line with the surface of the top ring.
 
Yeah agree with all the replies.... I get the mechanics and how it could potentially damage it.

I'm really interested if anyone has actually experienced or seen that damage. There are some very confident statements like "if you shim more than 0.025", you will damage your tube" and I can't find a single picture or first-hand account of someone doing it. Like where did that very specific number come from :unsure:
 
scotteboy said:
I shimmed the front scope mount after dropping and bending an old bushnell scope.
It worked fine untill I replaced it but I used a piece of plastic that was too narrow and it left a dent in the tube.
I didn't really care as it was a cheap scope but would have a shim the width of the scope rings in the future.
It was a "for now" fix. I'd be inclined to just replace what was needed these days.
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How thick was the plastic (if you can remember)? I'm actually shimming under the base of these rings so I wouldn't anticipate any tube damage from the shims themselves but people do say that it could crush the tube due to miscentering of the rings. My personal feeling is that the rings have bad tolerances and that shimming them actually would be better for the scope alignment....
 
I have never actually damaged a scope by shimming.
When I had my shop I saw scope tubes damaged by misalignment, poor fit, etc. Tubes marked, imprinted. Don't recall a scope's optical function being destroyed.
Something to think about - mount the rings on the tube. They are aligned. If the rings don't attach to the bases with neutral alignment, and the rings are pulled up tight on the bases, the scope is going to get tweaked.
The Burris Signature ring system allows the scope to be mounted in neutral, with no twisting or bending stresses.
 
tibblet said:
Yeah agree with all the replies.... I get the mechanics and how it could potentially damage it.

I'm really interested if anyone has actually experienced or seen that damage. There are some very confident statements like "if you shim more than 0.025", you will damage your tube" and I can't find a single picture or first-hand account of someone doing it. Like where did that very specific number come from :unsure:
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Im shooting a 308 model 7 in Talley 1 piece ring mounts.

The rear ring has a piece of a coke can in it.

No issues so far and gave me the elevation cliks I needed.

Its been in there for 4 years.
 
OP, shimming bases can create distortion issues with the tubes of your scope, that will create a parallax issue.

It may be very slight and nothing to worry about, unless you're into precision shooting venues.

It's one reason why I like to use "one-piece" bases to mount the rings onto.

The one-piece ring base can be shimmed between the receiver and the base, at either end, which will leave the base straight.

With "two-piece" bases, one base ends up higher than the other, and that also means the bottom of the saddle of the base raised, will be higher than the other. When you clamp down the cap, the scope tube will flex accordingly.

An example, albeit much magnified, take a flexible tube, such as a garden hose, grasp it tightly with both hands, and move them. The same thing happens to the hose as will happen to the scope tube when it's forced to compensate for the difference.

All of the above comments have valid points.

The best solution, if you're going to use two-piece bases, is to use rings with inserts that allow the axis of their centers to align proportionately.

The other solution is to "let the flames roar" shape the bottoms of the base saddles, which the scope rests in, by using a mandrel of the same diameter as the scope tube, covered with valve grinding compound to "lap" them both at the same time, to align them to the axis of center, taking the negative forces off the tubes, as suggested by Tiriaq and others.

This will stop any "distortions"

Most tubes are flexible enough that they will not be damaged if shims are only a few thou, but I've seen some extreme cases, where the wrong bases were used and tubes were damaged.

You don't indicate "why" you want to shim your bases.
 
tibblet said:
How thick was the plastic (if you can remember)? I'm actually shimming under the base of these rings so I wouldn't anticipate any tube damage from the shims themselves but people do say that it could crush the tube due to miscentering of the rings. My personal feeling is that the rings have bad tolerances and that shimming them actually would be better for the scope alignment....
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I think I used a couple clippings off a zip tie. Probably a couple mill thick and maybe 3/16" wide.
I was new to mounting scopes and figured the main tube would handle it. Nope. Put a good dent in it. Still functioned fine though.
I always thought that if I were to do it again, keep the shim(s) the width of the rings, not too thick and torque to spec and would probably do ok.
Thank fak it was only a bushnell!
 
I think the "why" is pretty standard and I wasn't really looking for a big discussion on "how to shim" or "pros and cons of shimming" or needing any help on the current project. I've exhaustively read all those discussions already ;). Just interested if there's any real evidence on the internet anywhere since I couldn't find any.

Anyway since you're curious, I picked up a set of burris tikka t3x rings, and am trying to mount an Athlon Argos BTR2 on my T3X. When mounted and bore sighting, I have to crank the elevation all the way up to get it to zero, leaving a measly 0.3 mils of adjustment room left.

The problem with the burris t3x rings is that the front ring is different from the back ring (it has a little post on the bottom that slots into the T3X rail). So, options are extremely limited. I can't swap the rings around (switch front and back) and I can't even change the position of the front ring along the rail, it's fixed. All I can do is change the position of the back ring, and shim it.

I've mounted other scopes on it fine with Talley rings so I highly doubt it's the scope or the rail. I could do more swapping around to isolate the problem but it's not really worth the time and i'm happy with my other scope setups and don't want to disturb them. Shimming under the back ring base with some aluminum has given me about 6mils of upward adjustment room so I'll take it out tomorrow and see how it does at 100yd. I'll be sure to let everyone know if I damage my tube. :LOL:

Ultimately i'm not super satisfied as I should have a full 9 mils up and down, but ill see how it does and re-evalute whether I want to buy Yet Another Set of Rings.
 
Its like the 556 in a 223...SAAMI says pressures too high thousands say your gun will blow up.

I bet you can't find one article or any proof its actually happened
 
over a few years I have seen a few scopes with dinted tubes, most from misalignment of rings .
I have seen some mounts that should have never been mounted on a gun, a couple where soldered on.
Then you have the hose clamp mounts on old 22's.
 
I feel that Burris Signature Z rings are the answer for most people.

If I need to 'shim', I do it with epoxy. Alignment bars can be handy for diagnosing these problem, but aren't required. Typically I'll mount one ring (usually front) to the receiver and locate the other with set screws in the receiver. Install the scope in the rings and tighten the ring caps, looking for a gap between the 'unfastened' ring/base and the action. This gives me an idea of how much epoxy I need.

I'll loosen off the cap of the ring that is fastened to the receiver, and remove the scope, leaving the ring I want to bed attached to the scope.

At this point I can smear some release agent on the receiver, apply epoxy to the base of the ring and then re-install the scope. Tightening the ring cap on the ring attached to the receiver leaves the other base floating in epoxy and ensures perfect alignment as both rings are attached to the scope, but only one base is attached to the receiver. Once the epoxy cures, swap out the set screws for the proper fasteners and voila, perfect alignment.

I'm not a fan of lapping. When properly aligned, modern precision rings do not require lapping. Many manufacturers recommend against the practice.

All that being said, if it's an elevation issue that leads you down this path, stop and read the scope's manual. Sometimes the remedy is as simple as adjusting the zero stop on the scope!

I've seen many damaged scopes, and even messed up a couple myself due to poor alignment. I'd like to think I have learned from my mistakes!
 
I’m not a gunsmith but have I seen damages scopes from improper mounting, yes.
One came from a retailer, offered free scope installation when buying a rifle package…wasn’t a great deal in my opinion.
I’ve even seen a guy struggle to make paper then after half a box of ammo he asked if I wanted to shoot it to see if it was him, I obliged but when I got behind it the scope fell off…so no need to shoot it, same shop did that one…they’re closed now.
Directly from shimming, no.
From misalignment due to a variety of factors, yes.
I would think though that damage would relate to the sum of multiple inputs.
Some scopes have thinner or multi piece tubes that would yield to the misalignment.
Extra screws and or elevated tightening force would apply more crush.
Combine the two and the outcome is obvious.
I would suspect in most cases of slight misalignment with most scopes using light clamping force they just get away with it, at least to some degree. If it’s slight, and the rifle holds zero, and the image is viewable how many people take their scopes off just to check or how many have the same scope on two rifles to compare; I’m thinking very few. Most people have their scope mounted for them and live with the results without knowing if any such issues exist except in extreme cases.

Checking alignment is super easy, lapping to correct a small indifference isn’t that hard.
Or insert rings are the easy button. Burris Signature Z rings, or their tactical XTR rings or if you have a Sako their Optilock rings all use polymer inserts that act like an orbital bearing correcting any misalignment and can be used with offsetting inserts to add elevation adjustment or correct other POI issues. Nice part is they absolutely will not mar a scope tube.
I don’t get the suggestion of putting anything in the ring…under the base I get but correcting the misalignment (lapping on non insert rings) would be something I would do, as well as lightly chamfer the ring edges after lapping (they can get sharp).
 
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