How does shimming a scope affect bullet trajectory?

[Starslinger]

I have a scope that sits 3 inches above the bore of the rifle. There is not enough downward elevation on the scope to zero the scope - it is shooting several inches too high. I have never done this but in theory if I shim or use adjustable elevation scope mounts so that the front of the scope is higher than the rear, I will be able to lower the point of aim/impact for the bullet and zero the scope, correct? So, how would that affect the trajectory of the bullet? How do I determine the bullet drop at various ranges for target shooting? Can anyone link me to a web based trajectory calculator that allows me to input the amount of shim and then calculates the trajectory? Thanks for any help!

[CoopsDad]

Is it a new or used scope? You may need to "center" the crosshairs by dialing it up to full top of its elevation adjustment, then dialing it to full bottom of the adjustment while counting rotations. Then dial it back to the halfway mark.

[Scratch705]

wait, you can't get the scope to adjust low enough to zero, and you want to lift the front up?

wouldn't you need to raise the rear of the scope in order to be able to zero?

[hermosabeach]

take a step back

Do you have a flat or MOA base?
MOA base adds 20-60 MOA for shooting long range

can you provide
rifle type
base type ring type and scope info?

"3 inches above the bore of the rifle"

can you get a cheek weld?

maybe a pic too

[hermosabeach]

scope

wait, you can't get the scope to adjust low enough to zero, and you want to lift the front up?

wouldn't you need to raise the rear of the scope in order to be able to zero?

lifting the front is correct...

extreme long range the scope is angled down.... you have to bring the rear down... or barrel up

[Foothills]

Burris makes mounts that help with this.

https://www.midwayusa.com/product/1548235656/

[Starslinger]

Thanks for the responses and the tips about the Burris mounts and MOA base. I think that discussing the exact type of rifle would be a distraction from my original question. I am willing to buy different scope rings - maybe I get get the ones from Burris. Let's assume that there really is no more downward elevation adjustment since I've already had two gunsmiths take a look at my setup and they said there was no more downward elevation adjustment.

But does anyone know how angling the scope might affect the bullet trajectory? I use the Ballistic Calculator by Gundata.org but I don't know it this calculator can factor in an angled scope, or if that needs to be done. Thanks again for all replies and any help!

[hermosabeach]

mounts

Burris makes mounts that help with this.

https://www.midwayusa.com/product/1548235656/

until you identify the issue, no need to buy items

[pohorsky]

How does shimming a scope affect bullet trajectory?

Too many variables. Your dealing with angles and fractions thereof. Distance between scope rings along with thickness of shims determines angles of adjustments. What moa adjustment does your scope have and how much more do you need? If you can't lower the scope maybe a 20 moa will help.

Kind of splitting hairs, but scope has nothing to do with bullet trajectory.

[audiophil2]

Not to be a jerk but it seems you have no idea how to make this work. Based on that it is easier if we all dumb this down a lot because trying to help won't work if you don't understand verbage.

Easiest start is if you provide a profile pic of the rifle about 3 ft away and then a close up profile so we can see the scope and mounts.

I won't waste time with the gunsmiths. I always assume they're clueless.

If you can't provide pics then we need to be as clear as possible or use a generic pic se we can identify and define the parts we need to address.

Btw, I shoot out to 1 mile and typically am 1/3 moa on my rifles. It takes me an hour to mount a scope with multiple levels and a heavy sled locking everytdown to make sure all.is plumb. Without a perfect zero a 1 mile shot can be many feet off.

[Foothills]

It's physics!

But does anyone know how angling the scope might affect the bullet trajectory? I use the Ballistic Calculator by Gundata.org but I don't know it this calculator can factor in an angled scope, or if that needs to be done. Thanks again for all replies and any help!

The scope has no effect on bullet trajectory. It's physically independent.

It changes the angle of the scope relative to the barrel. That changes the apparent point of aim when you look through the scope.

The Burris scope model for example would raise the back of the scope by a certain amount and lower the front of the scope by the same amount. This lowers the point of aim for the scope relative to the barrel. The bullet will impact higher in relation to the scope point of aim.

You do need to decide what range to zero at. The Burris mount has different thicknesses of inserts to adjust the scope physically.

You may want to first look into how the internal mechanics of scope adjustments work for your particular scope. The mount adjustments are pretty straight forward in comparison.

https://scopepicks.com/rifle-scope-adjustments-work/

[sacrvrrat]

Shimming a scope base is really no different then using an MOA base. It might not be the best way to solve your problem, but it can be done and not cause any other issues if done right.


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[SkyHawk]

The calculations are no different really, just use an accurate height over bore for the objective lens and any ballistics calculator. Shimming the scope is no different than turning the elevation turret, I am not sure why you'd want some different calculation

[baih777]

Need a pic of the scope mounted on the rifle.
Scope.brand name and model.

You may get lucky and all you need is a 20 moa scope mount.
But it does sound like your scope is mounted too high.

Shims wont fix the amount of adjustment you need.

[kcheung2]

1) It's a AK & a Leupold VX3 4-14x40 on a RS Regulate mount. See:

https://www.calguns.net/calgunforum/showthread.php?t=1784324

2) Have you fixed the scope? Based on that other thread you were having lots of problems with the scope turrets so it's very possible that with a functional scope you won't even need to get into shimming.

3) Your question is backwards. Angling the scope does not affect bullet trajectory at all, the trajectory is independent and will do what it does. The purpose of adjusting the scope is so it aligns with the bullet trajectory - whatever it happens to be - at a specific distance (your zero). Likewise, you are not changing the point of impact of your gun, you need to raise your point of aim.

4) Continuing with the theme from above, try going backwards. This sounds simple, but since you maxed out the knob in one direction, have you tried turning the knob the other way? There was another thread a few weeks ago where a person had a similar problem, the adjustment was maxed out. After some digging, it turns out he turned it the wrong way. So yeah, if you're new at something and it's turning out wrong, try doing the opposite. After all, it worked for George Costanza.

5) Yes there are ballistic apps which allow for an angled mount, but...
5a) the data is input as either MOA or radians...can you convert the thickness of a small sheet of aluminum into angular measurements? Sure you could math out cos theta = dist of rings/thickness of aluminum, but there's a big risk of significant digits and rounding errors. (I think that's the equation but double check my trig concepts)
5b) Assuming you overcome 5a, the output is given as an adjustment to your zero, but based on your other thread it doesn't seem like you have successfully zeroed your scope. Any adjustments from a wandering zero is just blasting into a hill.

If you think shimming might work, then just do it. Then take it out and see if you can zero it in. No need to overthink it. But even this simple step is predicated on having a scope that isn't broken, and that question has not been answered.