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Old October 11, 2018, 01:04 PM   #1
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scope ring lapping ?

How important is scope ring lapping ? I have never done it and never had a problem. Curious how many of you guys do it ?
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Old October 11, 2018, 02:11 PM   #2
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If fifty years of mounting scopes I had to do it once. The receiver wasn't drilled quite right on a Browning/Miroku Low Wall I had and the rings didn't line up. Lots of guys do it on every scope they mount. I've never damaged a scope by not doing it. If the scope doesn't sit in the bottom half the rings there's a problem. I don't think it ever hurts to do it if that helps.
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Old October 11, 2018, 03:58 PM   #3
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,,,,just buy DNZ scope rings.
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Old October 12, 2018, 08:18 AM   #4
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It depends.

First ...If you DO lap,your lapping bar should be slightly undersize to the nominal ring dia. I use .005 undersize ground stock for SwissTurn machines.

The reason is,whatever grit size you use adds to the effective cutting diameter of the bar. .005 is pretty good for 320 grit.

I'm sure methods have changed since the 70's,but I was given a tour of a very popular Colorado based scope manufacturer's facility as I was considering their Toolmaker position.

Their one piece bases were being "precision machined" by women holding mill finish blanks of bar stock against a belt sander with their fingers.

I've looked at name brand scope bases where my eyes could see the contour cut to sit on the receiver ring was out of parallel with the top of the base.

The mounting surfaces of any milsurp or reblue are suspect.

Why do people true and blueprint Rem 700's,etc? They are made from straight tubing,yes? They warp in heat treat.

Is it necessary? Assuming its right does not make it right.

You find out with a few strokes of the lapping bar over the lower saddles.

If you get an even cut over the finish,you are good.

If I'm building a rifle,I set the receiver up on a surface plate and use an indicator to make sure the bases are straight and level.If they aren't,I recut them.

Myself,I don't pay the big bucks for a precision optic,built to tolerances in the tenths of thousandths to distort the tube clamping misaligned rings down on it.

FWIW,if you do flex the tube,it will probably occur in the turret/reticle area.

Might flexing be the source of adjustment and zero problems? Hmmm.

I float the lapping bar in the saddles so I know what I have.I don't guess or assume

Last edited by HiBC; October 12, 2018 at 08:27 AM.
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Old October 13, 2018, 06:13 PM   #5
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I have read articles and watched videos on lapping rings , I buy high quality rings Ken Farrell , no need to lap , when you have 100% contact on your rings and torqued properly your scope will stay positioned . With lapping you have to be careful not to remove too much material or your scope will constantly shift. I would suggest get a good set of rings with no need to lap. May cost more but makes live easier.
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Old October 15, 2018, 10:37 AM   #6
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As HiBC pointed out, it isn't just how well the rings are made, but whether or not the base and mounting points are true. Heat treating does warp the receiver a little, so if the bases are mounted to tapped holes in the receiver, there's bound to be a little misalignment of even perfect rings. Not the rings' fault. Lapping them then trues them to that receiver.

For that matter, if you have rails mounted on your receiver, you can bet nobody scraped those true to a surface plate, either, and that if they are screwed tightly to out-of-true points on the receiver, they will be slightly bent by that, too.

I'll move this thread to the gunsmithing forum for you.
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Old October 15, 2018, 10:58 AM   #7
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As an do you lap vertical split rings?
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Old October 15, 2018, 11:15 AM   #8
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Old October 16, 2018, 06:54 AM   #9
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Scope ring lapping--something I've never done. Guess I've just been lucky for 1/2 century of using optics.
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Old October 16, 2018, 07:08 AM   #10
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Like a lot of things in shooting, random distribution determines whether you need to make the additional effort or not. Never say never. That "need", in turn, is different from wanting to do something that isn't strictly necessary but that may improve that last thousandth of precision. For that reason, scope ring lapping became common practice among those building rifles for benchrest competition first.
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Old October 31, 2018, 09:20 PM   #11
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I wonder how a person can know a lack of ring alignment issues without checking.

Unless a person has never had a scope problem of any kind,how can you know
ring misalignment was not the root cause?

"I've mounted "X" number of scopes for "Y" number of years,no problem....

Have you ever had a scope that had adjustments that did not repeat,or were erratic? You know,you chased zero around the target for 30 rounds?

Have you ever had a reticle fail?

Do scope manufacturers use superglue?

Take a tube and cut two holes through it for turrets and glue a sleeve over the outside.
Put the tube in two rings misaligned .003,will you notice as you torque 8 screws up to two white knuckles?
Will the tube flex in a smooth arc,or might the turrets focus the flex at the erector,reticle,and adjustments?.

I would not be so sure it never caused problems.

If you tend to lap your rings,and you notice 9 out of 10 times you neatly clean the blue off the Inside surface of the rings with your initial strokes,well,by golly,I'd say you have good reason to be confident.

But if you have never lapped or at least used an alignment mandrel to do you know what your alignment is?

I wonder if the same approach is ok for " I just build AR's by screwing in the barrel and throwing in a BCG . I don't use headspace gauges...been doing it 50 years,no problems so far.."

I have lapping bars,and I get some cut fairly often.Its not necessarily in the rings or mounts.
There is a reason Nesika Bay wire EDM's their receivers out of pre-hard steel.
Its the same reason some folks grind vee-flats on the outside of Rem 700 receivers for bedding. Warp in heat treat.. Perfect rings and bases can be mounted on a receiver that is not straight.
True,I have confidence in quality one piece ring/mounts for rails,

But,for example,two piece bolt rifle bases..better check.

Last edited by HiBC; October 31, 2018 at 09:28 PM.
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Old October 31, 2018, 09:48 PM   #12
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You're going to mount the rings on the rail, then the scope on the rings.
With a high quality scope, rifle and rings, they all *SHOULD* line up pretty closely, but like anything mechanical, there's a tolerance and none of it's perfect.

I found a slight "out of round" error when the rings were mounted, order of magnitude was 0.05mm. I gently lapped the rings and found the scope was less stressed, which meant that there would be less bending of the scope. The potential error at 1,000 yards is about 2 inches with a match grade weapon.
If you're shooting less than a few hundred yards or a non-precision rifle, it likely won't make as much of a difference.
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Old October 31, 2018, 10:14 PM   #13
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Have never had the need to do it in more than 50 years of shooting.
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Old November 3, 2018, 12:40 AM   #14
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Lots of guys do it on every scope they mount.
In over 30 years of smithing, I have done it exactly once because the customer demanded it. And I still have the lapping bar I bought from Brownells to do it hanging in my shop. Lucky? No, I just buy good rings and bases.
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Old November 4, 2018, 09:06 AM   #15
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This thread on screw torque specs is useful and adds the reminder to bed a base or rail to avoid it stressing the receiver should either be out of true. That reminded me of something I think M.L. McPherson wrote about using a steel rail to help stabilize some receivers. There is interaction here.

Most scope tubes can tolerate some degree of deflection stress before the insides get upset. If that were not true, scopes could not stand up to recoil. It would be interesting to know how much preload stress you can put on the tubes, but these things have been around for a long time and if actual alignment error damage were common, we'd all have heard about it. It's best to avoid it in principle, but saying that it's commonly necessary would be going too far.

As a check, you can use hi-spot blue or just smoke on your lap to look for uneven contact after you've aligned the rings. Set it into the lower rings under its own weight and slide it maybe a sixteenth of any inch back and forth, then look at it for rub-off marks. That will help you decide whether or not to mess with lapping.
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Old November 19, 2018, 02:49 PM   #16
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Even when using the so-called "good" rings, it doesn't take all that much time to push the lap back and forth to check how round the rings, both 1-inch and 30 MM, actually are:

I want at least 80% ring contact with the scope body, especially with the lower end rings. I don't want any scope sliding during recoil and scratching the scopes finish, or collapsing the scopes body due to over-torquing of the ring screws to keep it in place. Solid contact of the rings to the scope body, less torque needs to be applied, as there's maximum ring surface holding the scope. Doing the job right the first time only takes a little bit longer.
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Old November 20, 2018, 09:32 AM   #17
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I don’t lap the rings, or at least never have, but I do have one rifle that seems to kill/damage scopes. It’s a 223, so recoil isn’t the issue. I’ve swapped out scopes of 1 inch tube and 30mm tube, so it probably isn’t the rings themselves. I’m thinking that the action itself has some misalignment. I plan to lap that one if I have another scope problem.
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Old November 20, 2018, 11:16 AM   #18
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Purely a guess but thinking maybe 1 in 100k new scope rings get lapped. I have never heard of scope ring's that weren't lapped causing a problem! But then if you think you need to then you better!
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Old November 20, 2018, 11:46 AM   #19
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Totally logical, and a must.

I fully agree that two piece bases should at a minimum be checked. Smoke sounds like just the ticket to do that.

My take is that of the average shooter. I'm sure the long range crowd would gain more benefit vs. us average joes.
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Last edited by Ricklin; November 20, 2018 at 11:47 AM. Reason: typo
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Old November 21, 2018, 10:40 AM   #20
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I'll use inexpensive vortex rings(6 screw,alum.) $19.00 each on most hunting and varmint rifles. I put a lapping tool in and clamp it down with the top part of the ring and lap them in. When you do this you are matching the rings both top and bottom and they aren't interchangeable. Before you do anything with a ring you first have to determine what they are being mounted on and how true and straight this mount is. Rails are the easiest to work with because you can bed them ( bed the back end of them. ) Obviously, if your working on a $3000 rifle you might consider a top of the line mounting. I use Ken Farrell many times and especially their rails. I use a lot of Vortex optics. I try to keep cost into perspective but I don't compromise on accuracy or dependability. - This is what I do and it may not be suitable for you. If your budget prohibits all of this fuss, don't worry much about it. Just do what you can.
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Old November 21, 2018, 09:30 PM   #21
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Very entertaining post. For starters, what is to lose, by removing scope mounting pressures, which lapping does. Never had a problem? Sure, like not wearing your seat belt until you get thrown through the windshield! I guess it all comes down to what level of accuracy you are looking for.

Receivers are rarely 'true', so no matter how much you spend for wonderful bases and rings, you are tying them onto something a lot less than perfect. And that is what you will end up with.
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