Home Forums Hunting & Shooting Ask The Gunwriters Shimming a Scope

I took a new (to me) custom Springfield 1922 in .22 Hornet out to shoot yesterday. The rounds were landing approximately 7 inches high at 50 yards and there is no more downward adjustment left on the scope. Thus it appears that I'm going to have to shim the scope.

I'm assuming that I will need to add height to the front ring or under the front base (the bases are mounted on the receiver ring). Approximately how thick a shim would I need to insert and would I be better off placing it in the ring (and if so, how do I deal with the reduced interior ring diameter) or under the base?

Thanks.

I would shim under the base, try a .004 shim.

Soda pop or beer can material makes grate shim.

Yep, cans work great, and can be easily clipped to the right size.

Have also had good luck shimming the inside of the front ring with duct tape. You want to just place it on the bottom, not on the entire semi-circle. If one layer isn't enough, an even smaller piece can be added in the middle of the first one.

Shimming is also a good way to get ring marks, because if one ring is higher than the other the scope rides on the edges.

I do a version of what Mule Deer recommends with duct tape. I just put a piece of tape in the bottom, but not all the way around. Then I test fire. If all is good, I put epoxy in the ring bottoms and use a precision steel bar instead of the scope, release agent as appropriate. After the epoxy sets, I peel the tape out and fill the remaining gap with epoxy, placing the bar as before. If done carefully, you end up with perfect stress free scope contact in the rings. No metal removal is involved, and the epoxy can always be removed with a good solvent down the road, if desired.

This is what I do if Burris Signature rings with inserts aren't applicable. Works well for me.

Paul

Just went through the whole 'shimming' experience.

To 'lower' your POI, shim UNDER the scope on the front ring.

A soda bottle or other adult beverage aluminum can will give you a shim that will change POI about 4". Cut about 1/2-1" long strip, narrow enough to 'hide' under your scope. I'd think 2 shims, maybe 3 will get you where you need to be. Probably just 2.

I've used electrical tape on the lower ring-half, and it worked great.

That's if the rings were aligned and you shim them out of alignment. It seems that if he runs out of vertical adjustment then the rings are out of alignment already, and shimming would be bringing them in.

That's one way to look at it, but I don't know a precise way to gauge whether rings are in alignment to begin with. I don't trust rods, although perhaps they work if used correctly. What I left out is lapping as a first step. If you start lapping you see pretty quickly where the contact is, and it can be an eye opener. If they are out of alignment it will show as wear (bluing removal) on the respective edges. I have lapped a lot of rings, and can't recall any that started out in perfect alignment or contact. Maybe "good enough", but far from perfect.

If I can't use the Signature rings I usually routinely lap and epoxy bed, even if shimming isn't needed. Just gives me more confidence.

Paul

What type of bases are on the receiver? If they are anything "standard" I would seriously look at the Burris Signature rings with the plastic offset inserts. They do a wonderful job of correcting alignment issue of scopes, both vertically and horizontally (or a combination of both!). You can find a combination of plastic offsets that will allow you to keep the scope turret adjustments roughly centered so they aren't running near or at the limit of the internal springs. Plus they don't mark up the scope body and slippage won't be an issue on a .22 Hornet. Just my $0.02...

When I have this sort of misalignment, I generally use five-minute epoxy to bed the scope into the rings. If I need to raise the front ring, (and, in this case, it hasd to come up quite a bit) I cut a thin strip of business card which will lie in the front of the front ring. I then wax the scope tube, degrease the bottom half of the rings, mix the epoxy and put some on each ring. Then, put the scope in the rings (don't dawdle!) and snug the tops down (not too tight. just enough to bottom at the rear of the rear ring while the front is supported by the card). Let it set up for a half hour or so then remove the scope and trim off the excess epoxy and there you have it. The bottom halves of the rings will be perfectly aligned with the scope tube and the scope will be sitting in the correct attitude. GD

I've used soda can pieces wrapped in duct tape inside the rings when my $90 supposed to be high enough according to the web rings weren't high enough. Too frustrated.to send back and start over so just shimmer them. So far so good.

What Greydog describes is essentially the same as my method, but a bit simplified. I don't like the idea of bedding the scope directly into the epoxy. I worry about having it stick and needing to knock it a bit to get it free, so I use a length of precision ground 1" steel rod to form the epoxy bed.

Even that may not be a perfect fit. As Mule Deer noted elsewhere, scope diameters are not always true to spec. Folks, when you consider the various components made by different manufacturers, it's taking a lot on faith to expect everything to fit perfectly. There's this thing called stacking tolerances. Sometimes you get lucky, sometimes you don't.

Paul

A little something I've been playing with.



An old Balvar 8 with really clear glass. I use windage adjustable bases or rings and shim for elevation. I call it the "Turret Twisters Nightmare", you'd be surprised at the number of baffled shooters at the range when they notice there are no adjustment knobs on the scope. I've since moved it to a Savage 22-250 with Leupold windage adjustable base, shown are Weaver windage adjustable rings. I use greased hard paper shims(computer paper) they don't continue to compress over time and are easy to insert by just loosening the ring screws.

yes shimming works but i really hate to shim,i would rather get the right mounts for my rifles if i plan on keeping that scope on that rifle for a long time. scope mounts are not that expensive.

I've never owned the Weaver windage adjustable rings. When I look at them I conclude the design is flawed. It seems to me that if a set were mounted on a one-piece base (or the top of a flat top AR type rifle, or a two-piece base well anchored so as to act as a one-piece base), adjustment would create two axis that were parallel, but not collinear. If so, this would torque the scope tube, and possibly lead to ring marks.

However, I should make it clear that I never purchased a set of rings and tested them to see if I am correct. I have the education and experience to believe I am correct, but I will not state it as fact unless I am more sure.

Redfield style windage adjustable rings are supposed to allow the front ring to rotate to "point" to the rear ring. The rear ring should theoretically not turn to "point" toward the front ring, but it appears to me that there is enough "flex" in the design to minimize the issue. I don't see much "flex" in the Weaver design to allow the rings to align. (I don't like the Redfield system, but mostly for other reasons.)

All that said, I really do like the "plain old Weaver" rings and bases, especially the steel bases. But I remain skeptical of the Weaver windage adjustable rings.

Another bad point about the Redfield windage adjustable system is the adjustment screws have less purchase on the bottom of the ring when they are adjusted away from center. The adjustment screws move on a line left-right, but the rear ring moves in an arc.

Absolutely. That is what I was alluding to above. If the rear ring turns as it move laterally (following the arc you mention) to continue to point toward the front ring, then either there is enough slop in the threads or flexibility in the windage screws to seat correctly with the bottom of the ring . . . or not.

If things are not designed to line up correctly (Burris Signature system, rings reamed and/or lapped, scope epoxy bedded in the rings, whatever the method that ensures alignment), then the mount is going to try to bend or kink the scope tube. Depending on how stiff and strong the scope tube is compared to how much "leverage" the particular mounting system has, this can be bad or not so bad. But however it works out, it is not optimum. It has always seemed to me that even if the scope is not overly compromised, the whole deal is not a good candidate for holding zero.

Been gritting my teeth but can hold it no longer. If a scope won't zero something is wrong between the scope and the rifle (assuming the scope is good). If you shim it there is still something wrong between the scope and the rifle. Petty little things like that wear on me. Silly I know but I feel much better with things done "right."

Yes it does. Cuts easily with a scissor too.