Shims for a Scope

Sometimes when you mount a scope – something just aint right and you can’t get the scope aligned properly to get it bore-sighted.  Slight errors in the making of the base or rings or something…  Many reasons… but the result is that to get the scope bore-sighted right, you have to shim the scope.   Don’t panic.  And don’t go off and order some expensive Shim Kit.  And don’t use Paper shim.  They compress and get thinner over time.   You don’t need to spend any money… well, maybe 75 Cents at most.  You can make your own Shims.   It’s easy to do, and I do it all the time.  I am a professional, and I’m telling you – you can do this at home.  It’s Ballistic Science, but it’s not Rocket Science. All you have to do is to make some Beer Can Shims.

Now, they are called Beer Can Shims, because that’s what they were called when I learned of them… at Ft. Benning.  They called them that, because that was what they used.  They specified the use of Bud Light cans, but you can use Miller, regular Bud, Guinness, or any variety… for Mormons, you can use Mt. Dew, Coke, Pepsi, Full Throttle, Monster… because really, the brand is not important – but a Benning the SOP was Bud Light.  Just sayin.  Personally, I prefer Rockstar.

Pro-Tip: Wash the can out with hot water and dry it.

You use some shears, open the can up, and cut off the tops and bottoms.  Trim up sheet and section it, then cut it into strips.   The width and length are up to you.  1 inch tubes will use shorter ones than 30mm tubes.

If you make enough, you can go all Rip Taylor with them.

When you put them in the ring, under the scope, check the bore-site to make sure that you get the right amount.  Don’t use more than 4 shims.  If you need more than 4, you need to rings and bases or there is something wrong with the gun.  Typically I use no more than 3. When stacking them, but down a long one, then a shorter one on top, then a shorter one than the last.  You don’t want to shim the sides, just the bottom.  If you are shooting too low, shim the Rear.  Too high, shim the front.  Simple stuff… unless you get it wrong.


17 thoughts on “Shims for a Scope”

  1. What about the Burris ring inserts? Have you used any of those? Sure they’re more expensive(by a long shot) But I’ve used them with excellent results, and as an added bonus, they don’t mark up the scope tube at all.

  2. I’m a 35 year machinist and I have shimmed many many things with aluminum cans. The material is about .001 thicker at the bottom of the can than at the top. You can use that difference to make fine adjustments in shim thickness.

  3. I never shim in the rings. always shim under the base. tin foil works well as well as aluminum can material. foil is easy to start screw holes in. try 3 layers of foil to start.

    1. There are so many reasons that shimming the base is a bad idea. But I’ll start off with Recoil shearing the tiny screws that are now no longer going as deep into the receiver as they should.

      1. Mounting screws and receivers are always manufactured at least 0.01 deep/long to allow for this very very common needed correction, most parts sellers have “shim kits” to do just this.

  4. I’m 3inches below target on my vertical axis. I’ve put 3 shim (aluminum can pieces) underneath the rear base (eyepiece) side and the gun. Thus raising the rear up. I had to do this because I no longer can turn the “u” any further. Does anyone know an estimate of distance per shim I can recover?

      1. Sorry, I could have provided that info. I guess I was looking for an estimate based upon you guys experience. I went to the range yesterday. Here is the data I collected.

        25yd range
        Remington 7400 (30-06) Semi Auto
        I replaced an older Leupold with a new Nikon Monarch 3 (5-20×44)
        I kept my old Leupold rings and bases. I assume they are Leupold. There is a set screw in the rear mount to keep the ring secure against the base.

        I used a 6oz coke can since my kids drink these little drinks. I wasn’t sure if that is the same thickness in aluminum as the regular size. So, I cut a piece out and did a trifold (3 layers). I placed between the base and ring where the screw holds together.

        At 25 yds with the vertical “up” maxed out, I was 3 inches low before the shim. After the shim, I was 2.5 inches high. So to answer my own question, I gained about 5.5 inches over all with approx 3 shims at 25 yards. This allowed me to use the down now to fine tune back to where I wanted to be at that distance. Thanks, for checking. Hope this helps someone else down the road.

        1. Ah. Well, there is your problem. You need to zero that at 100 Minimum. I’d suggest zeroing at 200 yards actually. But at 25, yeah, you are not going to get that right – and you don’t want to. Ideally even at 100 yards, you should be hitting 1″ to 1.5″ high.

  5. Hi, I have a question on how many shims to use as well. I have a (almost new) ’80s Marlin model 60 (.22). I got a new Bushnell Trophy XLT 3-9×40 scope. It was laser bore sited and seemed on, but when I got the range, it’s vertical was already maxed out and I was 4″ to 6″ low (I didn’t think to measure it at the time) at 50 yards. The old Tasco Rimfire 4X15 scope was close to bulls eye. Cabela’s thought there was something wrong with the scope and pulled it so i could send it in, but now I’m thinking I should just use some shims. Bushnell wants me to pay for shipping both ways, and I only payed $50 after the sale and rebate, so I don’t want to pay $20 more in shipping for them to tell me to shim it. Sorry for the rant. How many shims do you think? I have pop cans and I have printing plates which are .3mm (.0118″) thick. I do plan to site it at 100 yards eventually.

    1. No, that wont work. You’ll have to use windage bases. Which isn’t bad. Get blue Loctite in the stick form, and before you zero – hit that on the windage adjustment bolts so once you set it – it’s going to stay. Also, before you do that – find the mechanical zero of the scope so it’s dead nuts centered before you start. Adjust windage with the base roughly and let it set there. Fine tune the zero in the scope.

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