I bought an old hunting rifle and after shooting it I discovered the scope can’t adjust its elevation low enough with its current mounting. I want to avoid buying new mounts, so with some research I’ve read online you can shim scope mounts to correct this. At 100 meters it appears to be 5 inches low, can shimming correct this? Any advice on how to proceed would be appreciated!
Need Advice on shimming a scope
- Thread starter Middlebacker45
- Start date
If you have a one piece rail, you can shim the back end. There's a bit of math involved though.
Measure the distance between your scope rings in inches. Multiply that by two, then multiply that answer by 3.14159 (pi, or π), divide by 360 (degrees) and divide again by 60 (arcminutes). The result is shim thickness in inches-per-one-MOA.
If you have split bases, shimming the rear base will put a tiny bit of torque on your scope tube. It may or may not have a noticeable effect on your scope. It's generally not a good idea, but I also know a couple of people who have had success doing it that way.
Measure the distance between your scope rings in inches. Multiply that by two, then multiply that answer by 3.14159 (pi, or π), divide by 360 (degrees) and divide again by 60 (arcminutes). The result is shim thickness in inches-per-one-MOA.
If you have split bases, shimming the rear base will put a tiny bit of torque on your scope tube. It may or may not have a noticeable effect on your scope. It's generally not a good idea, but I also know a couple of people who have had success doing it that way.
Make sure you're reading the scope right as in the previous post. The "up" and "down" written on the scope moves the bullet pattern up and down.
What type of rifle is it? You could have the wrong bases. Shimming should be done as a last resort. If you need to shim, cut some pieces off pop can and place into the scope rings. Put blue Loctite on all mating surfaces. Getting 5 moa out of it may require quite a bit of shimming - your scope may not hold zero with that amount of shimming. Uneven grip on the scope also risks damaging it during heavy recoil.
Epoxy bedding the bases to slope upwards is the proper solution. Or get a scope with more adjustment.
What type of rifle is it? You could have the wrong bases. Shimming should be done as a last resort. If you need to shim, cut some pieces off pop can and place into the scope rings. Put blue Loctite on all mating surfaces. Getting 5 moa out of it may require quite a bit of shimming - your scope may not hold zero with that amount of shimming. Uneven grip on the scope also risks damaging it during heavy recoil.
Epoxy bedding the bases to slope upwards is the proper solution. Or get a scope with more adjustment.
There are many different ways to accomplish this with scopes that don't adjust enough on the elevation turret to put your rifle on target.
The most simple method that I’ve found is to add a piece (or two) of scotch tape or electrical tape under the rear scope base. If that doesn’t achieve enough adjustment, manufacturing a shim is possible. However it might be a lot of trial and error (resulting in lots of time spent and wasted rounds down range). It might also open up a can of worms.
Your mount screws are likely going to be too short to pass through both the mount and shim to engage properly into your action. You might just sheer off your screws when firing your gun and/or you may need to find longer screws for full, proper mounting.
The second issue you might encounter by adding a single shim is misaligned of your scope rings. It could put undue pressure on your scope or might result in a damaged scope or severe ring marks. However, this can be corrected by lapping the scope rings after you install the shim.
But, before you go down that road of shimming your existing mount, (and one of the best and easiest solutions to your problem) might be to purchase a set of Burris Zee Rings with variable plastic inserts. I’ve used these rings for your exact issue, and they work great.
https://www.burrisoptics.com/mounting-systems/zee-rings
The most simple method that I’ve found is to add a piece (or two) of scotch tape or electrical tape under the rear scope base. If that doesn’t achieve enough adjustment, manufacturing a shim is possible. However it might be a lot of trial and error (resulting in lots of time spent and wasted rounds down range). It might also open up a can of worms.
Your mount screws are likely going to be too short to pass through both the mount and shim to engage properly into your action. You might just sheer off your screws when firing your gun and/or you may need to find longer screws for full, proper mounting.
The second issue you might encounter by adding a single shim is misaligned of your scope rings. It could put undue pressure on your scope or might result in a damaged scope or severe ring marks. However, this can be corrected by lapping the scope rings after you install the shim.
But, before you go down that road of shimming your existing mount, (and one of the best and easiest solutions to your problem) might be to purchase a set of Burris Zee Rings with variable plastic inserts. I’ve used these rings for your exact issue, and they work great.
https://www.burrisoptics.com/mounting-systems/zee-rings
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unstableryan
CGN Ultra frequent flyer
- Location
- Beautiful Okanagan Valley
Any possibility that front is in the back and back is in the front?
OkayShooter
CGN Ultra frequent flyer
- Location
- Nova Scotia
Also the bases could be drilled and tapped crooked.
Like my Mauser. If I run weaver rings and bases I run out of windage. I have to run Leupold or Millet turn in rings.
It’s an FN built Mauser 98 that’s been modified, only the bolt and receiver are original.
Remove the scope & rings from your rifle.
Lay a straight edge [metal ruler] across both bases.
Is there a gap between them?
If so, you've either got the wrong bases, or you need to shim.
Both bases MUST be in the same plane.
Lay a straight edge [metal ruler] across both bases.
Is there a gap between them?
If so, you've either got the wrong bases, or you need to shim.
Both bases MUST be in the same plane.
Not sure about the brand but it’s a single piece mount attached directly to the receiver, no rail.
Is it an FN commercial receiver [not clip slot on left hand side & no clip lips on tops] or an ex-military receiver with both?
Are there any identifying marks on the 1 piece base?
Is it a 3 screw mount [2 front, 1 back] or a 4 screw mount?
Does it take Weaver style rings or dovetail rings?
Are there any identifying marks on the 1 piece base?
Is it a 3 screw mount [2 front, 1 back] or a 4 screw mount?
Does it take Weaver style rings or dovetail rings?
If you can't post a photo, does it look like any of these?
Found a logo on it. It’s a Redfield mount, looks basically identical to the middle image. With what I learned from the responses I’ve received on this forum I think it’s already been epoxy bedded. Might just need to bite the bullet and buy a new base.
Remove the single rear screw. Does the rear of the base then "spring" up? If so, you can add a shim or 2.
If the POI is already 5" lower then desired, as long as the elevation turret can be turned counter clockwise, it will raise the POI to desired center.
If the turret is at the upper most part of its travel, then raise the front of the 1pc scope base until you can center the travel or have enough to solve your issue.
Maybe you have the turret position backwards? or a Euro spec turret (clockwise to raise poi)
Jerry
Next question is what scope did you have mounted? Could check how many moa it actually has for adjustments. While not ideal, some scopes only have 40moa vertical adjustment and some have up to 75moa. The latter one might be able to be zeroed.
