Scope Shimming

[Pirate69]

I think I known the answer to this but I am staring to second guess myself. I have a scope that has run out of "up" adjustment. It is hitting low and I can't adjust the scope up to the POI. Which mount needs to be shimmed; the front or the rear?

[williamwaco]

I think I known the answer to this but I am staring to second guess myself. I have a scope that has run out of "up" adjustment. It is hitting low and I can't adjust the scope up to the POI. Which mount needs to be shimmed; the front or the rear?

Same as with iron sights.

Move the rear in the direction you want the POI to move.

or,

Move the front in the opposite direction.

Be careful. If you shim too much, you can bend your scope tube.

[slim1836]

What he said ^^^^^^^^

Shimming the rear mount up makes the scope look down more which in turn raises the barrel end up.
Just a business card thickness worked for me.

Slim

[fouronesix]

^ all good advice!
Usually if a scope has run out of vertical adjustment, something is "kattywompus" with the rings/bases or the the gun. Some guns, including milsurps, that have been ground or modified are odd anyway and correct rings/bases may not exist. Those usually call for custom bases. It would be better to solve the problem with correct rings/bases than by shimming. In any event don't over-shim…. as has been posted.

[country gent]

My long range rifles scope mounts are 20 mins built into the mount. The riser rails I made for my ARs are 10 - 15 mins built in elevation and the iron sight mount for my warner rear built into them. Shim the rear up and if possible relap the rings into alighnment before re mounting the scope. If you can get on paper this will give you an idea how much shim you will need, Error in inches X sight Radious in inches ( distance between rings with a scope) / range in inches. Another thing is its easier and much neater to use one shim than a stack of them. Blacken the edges of the shim before installing it also.

[lefty o]

pick up a set of burris signature series rings, and be done with it. that way you have no worries about killing a scope from the front and rear bases being out of alignment.

[Cap'n Morgan]

A hint for adjusting sights in the right direction, whether it is the front or rear sight (or a scope to be trimmed):

Simply imagine you move the sight in question a copious amount up/down or left/right - like a couple of inches - then you just imagine lining up the sights
and notice in which direction the barrel is pointing. Simple, not? ;)

[B R Shooter]

pick up a set of burris signature series rings, and be done with it. that way you have no worries about killing a scope from the front and rear bases being out of alignment.

This is the best answer. Many things can be out of alignment to cause the scope issues, where the scope doesn't have enough adjustment to correct it. Without finding what is out of alignment and fixing that, the best things are the Burris rings.

Shimming a scope ring changes the internal diameter too small, and something has to give, which will be the scope barrel. Plus it takes the other ring out of alignment with the shimmed ring, and will surely scar the scope.

[John Taylor]

I have seen lots of guns with shims to get the scope lined up right. A drop of Loctite will keep things from moving around. You can make shims from pop cans or buy a set here http://www.brownells.com/gunsmith-tools-supplies/sight-scope-installation-tools/scope-shims/hart-scope-base-shims-prod6883.aspx

[725]

Burris makes a ring set that has asymmetrical inserts so you can adjust a whackey scope way off of where plain rings put it. I suggest looking into them. It's easy, clean, and just the ticket for your problem.

Basically you bring the scope to it's center (center adjusted for elevation & windage) and then install it with the asymmetric ring inserts. Adjust POI as you go. Once you have centered the scope, lock it down and make any final, minute adjustments with the scope's turrets. You can make any kind or combination of adjustments. High, low, left, right, or high right, high left, etc. that you need just by turning the inserts. You end up with no shims or other bubba like corrections and a perfectly centered scope. Until these came along, my adjustments, when needed, were pure bubba technology, which worked fine, but looked bubbaish.

[Hardcast416taylor]

An old gunsmith once told me about shimming a scope. "Either get a new scope or different mounts, `cause somethings not right". As to shims he said to use metal from a beer or soda can, card paper can draw moisture.Robert

[swheeler]

This is the best answer. Many things can be out of alignment to cause the scope issues, where the scope doesn't have enough adjustment to correct it. Without finding what is out of alignment and fixing that, the best things are the Burris rings.

Shimming a scope ring changes the internal diameter too small, and something has to give, which will be the scope barrel. Plus it takes the other ring out of alignment with the shimmed ring, and will surely scar the scope.

I've never seen anyone shim inside the ring, add shim stock UNDER the base. OP needs to shim the rear base

[Larry Gibson]

Yes, you should be shimming under the base, not inside the scope rings.

Larry Gibson

[M-Tecs]

Not that well made but they really work well. None of the issues with shimming.

http://www.burrisoptics.com/sigrings.html


Posi-Align Offset Inserts
By utilizing ***-Align Offset Inserts in Signature Rings, you can virtually sight-in your gun without moving the scope adjustments. By keeping the internal optics centered, you'll see through the scope all of the clarity, sharpness, and brightness that the optics designers intended for you to see. The offset inserts also correct for any misalignment caused by receiver holes drilled off center, or the bases or rings being slightly off perfect center. And for you 1000-yard shooters, the need for expensive tapered bases or shimming becomes a hassle and expense of the past.

[swheeler]

Not that well made but they really work well.

http://www.burrisoptics.com/sigrings.html


Posi-Align Offset Inserts
By utilizing ***-Align Offset Inserts in Signature Rings, you can virtually sight-in your gun without moving the scope adjustments. By keeping the internal optics centered, you'll see through the scope all of the clarity, sharpness, and brightness that the optics designers intended for you to see. The offset inserts also correct for any misalignment caused by receiver holes drilled off center, or the bases or rings being slightly off perfect center. And for you 1000-yard shooters, the need for expensive tapered bases or shimming becomes a hassle and expense of the past.


Yes they do look like an easy way to acomplish windage or elevation adjustment

[B R Shooter]

You cannot in any way shape or form deny shimming the inside of a scope ring changes the inside diameter. It is done all the time, and scopes are damaged all the time. The proper way to fix the problem is to shim the proper base, then lap the rings. The Burris rings are the best thing since sliced bread. And, if you want more elevation, they sell inserts that have more offset.

[Larry Gibson]

Not that well made but they really work well. None of the issues with shimming.

http://www.burrisoptics.com/sigrings.html

Posi-Align Offset Inserts
By utilizing ***-Align Offset Inserts in Signature Rings, you can virtually sight-in your gun without moving the scope adjustments. By keeping the internal optics centered, you'll see through the scope all of the clarity, sharpness, and brightness that the optics designers intended for you to see. The offset inserts also correct for any misalignment caused by receiver holes drilled off center, or the bases or rings being slightly off perfect center. And for you 1000-yard shooters, the need for expensive tapered bases or shimming becomes a hassle and expense of the past.

Just make sure you lock 'em down with loc-Tite or something else if mounted on a medium to heavy recoiling rifle. They will shift otherwise. Had them on my M70 Classic Sporter 30-06 with a Zeiss 3x9 Conquest scope. The zero kept shifting (groups were still nice) and it drove me nuts until I questioned the mounts. Replaced them with standard Leupold base and rings, shimmed the rear of the base for max scope elevation adjustment and life has been good ever since. The more moving parts you have the greater the odds something will go wrong.

Larry Gibson

[swheeler]

You cannot in any way shape or form deny shimming the inside of a scope ring changes the inside diameter. It is done all the time, and scopes are damaged all the time. The proper way to fix the problem is to shim the proper base, then lap the rings. The Burris rings are the best thing since sliced bread. And, if you want more elevation, they sell inserts that have more offset.

I've never seen anyone try shimming the inside of a ring, ever the ones I know that are, shall I say challenged. I guess I hang around a smarter crowd.;)

[Pirate69]

Lots of great advice here. Thanks everyone. In my mind, I had already thought that something is wrong. I took another look at the Weaver bases that came on the rifle and I think the front base is incorrect; it may be a bit taller that another base that I compared it to. Need to check this out properly. Thanks again everyone.

[country gent]

Another thing to remeber is when setting a scope up with angled mounts to gain distance zeros is that it still zeros at the closest range you plan on shooting. With the scope on my one long range rifle it wont "zero" at 200 yds. It is around 6" high . But the 600 yd zero is close to centered and 1000 is only a little more above center of adjustment. Doing this and keeping scopes centered at ranges used gives the best view thru them and centered adjustments give fuller range of use. While most scopes are close to centered at 200yds a bottomed zero at 200 gives much more up adjustment and useable scope. To do this depends on rifle caliber and scope. 10 mins is a good starting point with most thopugh.

[TenTea]

Depends on the mounting configuration (OP didn't specify):
Picatinny rail
Weaver rail
3/8 dovetail rail
Receiver mount
Claw mount
Side mount

For me, a Picatinny rail base mount with 20 MOA elevation built in is the answer.

[HangFireW8]

Yes, you should be shimming under the base, not inside the scope rings.

Larry Gibson

That's right. And the purpose of shimming under the base is to determine exactly how much your gunsmith needs to mill the other end of the base.

[Pirate69]

Problem solved. I have a steel rod that I have "stuffed" into tygon tubing aand it is a perfect fit for a 30 cal barrel. Perfect protection as well. Placed the rifle in my rifle vise and leveled it so that a level across the scope bases was perfectly level. I ran the covered rod through the breach and out the end of the barre about 8 inches. The rod was solid without any movement. Placed the level on the rod and it was perfectly level. Rechecked the level of the bases; level also. Figured it is not a base problem. Changed scopes and now have all the vertical adjustment that I need.

Thanks again for all the advice.

[Safeshot]

I think that the "Burris Signature ZEE rings and inserts" (rather than the "Burris Signature Rings") are the rings and inserts to use. The (offset) spherical inserts are available in offsets to correct problems and to use for long range scoped applications while keeping the reticle at or near the mid range of the adjustment travel.

[Clark]

112250
Steve Acker published a pic ~ 10 years ago of him modifying the bottom of a Weaver base by using a boring bar in a boring head.

I get the radius, center, and height as close as I can with the mill. Then I put in tiny shims and then then glass bed the base to the receiver. When the glass is hard, I tighten the screws. The high end Mauser smiths don't like that, but the high end sniper smiths do. Too bad, I like Mausers better.