Scope mount shims

nairbg

nairbg

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I have just acquired a Winchester Model 70, in .223 Rem. It has a Leupold VX II mounted in Leupold rings on it. I took it to the indoor range today and found that this rifle shoots 1.5" low at 40 yds, at full "UP" adjustment of the scope. I make that about 10 clicks from where I would want it for 100yd sight-in.

This is the first time that I have run into this issue with a scope. My questions are:

Is it a "normal" thing to shim a scope mount to achieve proper position.

Is there some standard "shim thickness/MOA" that I can use to estimate the proper shim thickness I'll need?
 
It is not uncommon to have misalignment issues but with todays modern production it is less likely to have any significant misalignment. You might want to check that the bases are the right ones etc..

Many things can cause problems. Irregular polishing (prior to bluing) of the action, irregular bedding, wrong/modified bases, etc all can cause problems.

If you don't know the history of the scope you might want to check to see if it is bent. You can loosen the scope ring top halves and rotate the scope in the lower rings on the rifle or you can remove the scope and rotate it on Vee blocks. Often times if there is a bend in the scope you will see it with your naked eye . The eye piece or objective will look like it is moving up and down as you rotate it.

You can quickly check base alignment (elevation) by using a straight edge before the rings are mounted. At this stage you can correct some of the elevation misalignment.

Usually after installing the lower ings halves to the base and before mounting the scope, a lapping bar (with lapping compound) will quickly show the degree of misalignment.


Hope that helps....
 
If there is a mechanical misalignment, the Burris Signature rings with eccentric bushings can be a very easy solution.
 
The quick fix is to grab a one-piece base and some shims and raise the rear up about .020 thou and keep going if you need to get to the centre of scope elevation adjustment where you want. If you elect to stay with a 2 piece base, you need those Burris type bushing rings as posted earlier and raise the rear base the same, other wise you'll bend and/or break the scope.

You can always make cheap shims out of pop cans or any sheet metal you have on hand. Use calipers to measure the thickness. :)
 
I'm assuming your scope is mounted 1.5-2" above the bore? I'd try it at 100 before messing with shims. Remember, if your crosshairs are 2" above the axis of the bore, your bullet would have to effectively "climb" that two inches at 40 yards in order to be "zero'd" at that range.

Try it at a more reasonable distance for the .223 and go from there.
 
Wrong Way said:
I'm assuming your scope is mounted 1.5-2" above the bore? I'd try it at 100 before messing with shims. Remember, if your crosshairs are 2" above the axis of the bore, your bullet would have to effectively "climb" that two inches at 40 yards in order to be "zero'd" at that range.

Try it at a more reasonable distance for the .223 and go from there.
Click to expand...

Great!:eek:

Now you've done it!:mad:

Of course my assumption was that the scope was esentially on the same horizontal axis as the bore. Obviously this is an erroneous assumption. I'm glad that I did some linear algebra and basic physics, back in the day.......

Now where's my calculator???:runaway:
 
No need for a calculator...Just rounding to the nearest "convenient" #'s will tell you what you need to know....assuming a 2" varience, thats 2" of elevation you are trying to gain at 50 yds. This = 4 MOA. 2 clicks on your scope (assuming 1/4" adjustment) = 1/4 min at 50. Therefore, you would need to move it (4 MOA / 1/4 X 2 clicks) = 32 clicks (from center). If your scope has 1/8" adjustments, make that 64.

Rather than paying them to shim and lap, try it at 100.....then hold "off bull" when shooting at 40.

Ryan
 
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