Shimming scope

WhelanLad

WhelanLad

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So I've got this wrong and It hurts to use my brain this weekend but my Zastava 7.62x39 is shooting Low with 150gr SP load, an now the scope is Maxed out for "up" clicks.

I'm going to Shim the scope in the rings.
Alum can will be the material.

Where do I need to Shim to bring the bullet Up more.... scope down more.

Ps- I've already tried and it was wrong, so asking pro advice as if I hadn't tried it already 😂😁🫣
 
WhelanLad said:
So I've got this wrong and It hurts to use my brain this weekend but my Zastava 7.62x39 is shooting Low with 150gr SP load, an now the scope is Maxed out for "up" clicks.

I'm going to Shim the scope in the rings.
Alum can will be the material.

Where do I need to Shim to bring the bullet Up more.... scope down more.

Ps- I've already tried and it was wrong, so asking pro advice as if I hadn't tried it already 😂😁🫣
Click to expand...
 
Sounds like you have tried shimming with no success and hopefully no damage to the scope. Always shim under the scope mounts bases equally on a receiver that has no anomalies in surface accuracy. Not all scopes and mounts are correct for all installations something to consider. If scope is a one inch tube it may be advisable to experiment with a 30mm tube body that will have more usable adjustments available. Shimming under scope mounts will require more elevation adjustments so this is not an option.
Shimming under one base only(rear) can bend your scope body as there will be no flat straight alignment between front and rear base if using a two base system. One other test is to carefully exercise the adjustments in the scope by running the elevation and windage right and left; up and down a few times as there could be a minor hang-up in it's adjustments. Use a gentle touch doing this and no excessive turning near the ends of threads limits as this could do further damage. Going to lower mounts could remedy proving there is clearance for bolt handle. There are other considerations but this is a a suggestion to get you back on target. Anything further do not hesitate to give a call 705-879-1335. Ralph at Kawartha Arms. There could be issues with stock and there are a few checks for any issues; another subject. All for now.
 
There's always right and wrong ways to do things, and wrong ways that work.

A strip off a coke can on the rear ring has worked in the past.

One layer of coke can in the lower half of the rear ring gave me about a dozen or so clicks and brought me up and on target.
No scope damage has occurred.

I torque the ring halves to manufacturers spec. Usually 16-20 inch pounds depending on fastener size and ring material.

I've seen scopes with dents on the EE and at gun shows from over torqued rings that I wouldn't trust though.

LOL , a younger guy I saw at the range was obviously having issues with elevation and he was tightening his front scope ring with a Allen wrench and a 8" adjustable wrench for leverage , I'm guessing to force the objective end down.

Likely just crushing the tube.
 
So you taker a 1 inch ring that fits a 1 inch scope tube and you reduce the inside ring diameter with a shim... so you are clamping a 1 inch tube with a ring smaller than 1 inch.

What's wrong with this idea?

Shims should be placed between the scope base and the action. If it is a lot of shim, then the bases should be glass bedded with less than tight screws with the rings in place on a 1 inch bar... aligning the rings square to each other and a built in angle to the bases. Aftr all is cured all screws can be made tight.
 
Just like irons, move the rear in the same direction as desired poi shift
move the front the opposite direction of desired poi shift

is it a problem with just that one load or has the rifle always had poor results?
 
Last edited:
boxhitch said:
Just like irons, move the rear in the same direction as desired poi shift
move the front the opposite direction of desired poi shift

is it a problem with just that one load or has the rifle always had poor results?
Click to expand...
i hadnt noticed it too much but thinking back, i knew it was getting closer to running out of elevation clicks,....
then more recently i removed the scope and moved it back toward the eye / and off the rear sight, an re tightened.

i wanted to see if there was a change in poi after releasing the scope to slide back a few mm, then re tightening..... there was-

so i went to re zero and came up against A- clicks run out (basically at zero) and the B- the turret caps wont fit back on with them so extended LOL

nikon monarch 3-15x40mm tis a nice scope!

RE th above Bold text, ive done it the opposite way here-- that explains :p

Thankyou!!
 
turkeyhunter said:
Sounds like you have tried shimming with no success and hopefully no damage to the scope. Always shim under the scope mounts bases equally on a receiver that has no anomalies in surface accuracy. Not all scopes and mounts are correct for all installations something to consider. If scope is a one inch tube it may be advisable to experiment with a 30mm tube body that will have more usable adjustments available. Shimming under scope mounts will require more elevation adjustments so this is not an option.
Shimming under one base only(rear) can bend your scope body as there will be no flat straight alignment between front and rear base if using a two base system. One other test is to carefully exercise the adjustments in the scope by running the elevation and windage right and left; up and down a few times as there could be a minor hang-up in it's adjustments. Use a gentle touch doing this and no excessive turning near the ends of threads limits as this could do further damage. Going to lower mounts could remedy proving there is clearance for bolt handle. There are other considerations but this is a a suggestion to get you back on target. Anything further do not hesitate to give a call 705-879-1335. Ralph at Kawartha Arms. There could be issues with stock and there are a few checks for any issues; another subject. All for now.
Click to expand...
^^ This! You will see it go wonky on various ground receivers - think "sporterized" mil-surp rifles - the contours of the receivers are often not the same - one to another. The metal rings will be designed to hold that diameter of scope body - with an "air gap" (usually) between the top and bottom ring halves - as is mentioned, not real productive to alter that dimension. So, shim goes under the bases.

However, the top of the bases must make a "plane" - so, although a metal shim is placed under the rear base, usually has to be a taper shape and front ring underside also tapered - else the scope body bends, if two bases are both parallel to bore, but different heights. One piece bases not immune from that - they bend to match rifle's receiver contour when torqued up - ideally they need continuous taper shim from front of base to rear of base - I have had decent luck by "bedding" the base with epoxy and using a metal shim around the rear hole - in effect, the bottom of the base is "straight" - supported by the epoxy bedding - the base does not deform , twist or curve when the screws are snugged up. For two piece bases, I often hold rings onto a lapping bar - then set the rings onto the bases - to see what is needed for shimming / epoxy.

To measure if top of bases are a "plane" - I use a known metal straight edge - top of rear base - slide forward to contact front base. Once I think I have it correct, then top of front base back to top of rear base - then left sides to right sides - so end up with bases "square" to each other and in a plane to each other. Or, slap on a "store bought" thing and call that "good enuff". From my Millwright brother - if you can see light between a straight edge and a flat surface, you are in the arena of more than 10 thousandths of an inch gap (.0001") - for some that is too much error. You may want to file / scrape / polish underside of scope base to be that close.
 
As mentioned above, Burris Opti Lock rings are your best option, but they aren't cheap. $C150.00 appx.

There is another, cheaper option available to you.

guntech doesn't like the idea but "installing shims, usually brass, under the rear ring base is quite simple. I've used everything from stainless steel, brass shim stock and even Venetian Blind strips for shims, or you can find another base which is higher and "modify" it to the desired height.

There is much more to this than meets the eye.

You will have to "LAP" your rings, using a length of one inch round steel rod and valve grinding compound. You only lap the bottom ring base and leave the top covers alone. They will align properly when you screw them down.

You need to do this so the scope is laying "flat" in the rings, or the tube will be slightly bent, when you screw down the covers. This will cause slight image distortion and induce parallax, neither of which you need and it can't be dialed out.

When I do this job, I use a very thin strip of material, made of fiber, and sticky on one side, on the saddles of the bottom ring bases. This helps to keep things aligned and stress free.

It can be a tedious process, and it makes the cost of the "Opti Lock set" look cheap.

The Burris Opti Lock rings come with inserts which are self aligning, they also have different outside diameters, so you can lower the front and raise the rear optical center alignment, or vice versa.
 
As others have said. ( i've been drinking tonight) your rings are f u qu ed .
I'm sure I'm probably wrong (cuz I am sometimes) but it doesn't compute any other way for me. unless you have placed a set of 20 moa rings front to back. Cheers hope your havin fun like me tonight
 
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