View Full Version : Lapping of Scope Rings

Rich Lucibella
March 12, 1999, 07:52 PM
I've heard from one *very* reliable source that he will not mount new scope rings on a rifle without lapping the interior first.
Looking for more information. Rosco- that means you!

March 12, 1999, 07:57 PM
What the heck is "Lapping"??? And who is "He"???

Maybe this is one of those things that the general population of this message board isnt supposed to understand... hehehe

Art Eatman
March 12, 1999, 09:16 PM
Yeah, Rosco, answer Rich. I wanna know, too. At first blush, it sounds like a solution in search of a problem. Are manufacturers are getting real sloppy in their alignments and dimensions?

Rich Lucibella
March 13, 1999, 12:12 AM
Lapping is the same process as lapping valves in an engine. It assumes that cast ring interiors are not in perfect round....therefore, less than 100% of the ring surface will contact the scope.

Lapping a 1" ring consists of coating a 1" rod with an abrasive compound and turning it in the scope ring to "true" the orifice.

Dave Finfrock
March 13, 1999, 01:50 AM
Lapping the rings refers to truing the interior bearing surface up so the entire ring engages the tube of the scope. The idea is to have as much surface area of the ring as possible engaging the scope tube to prevent the scope from moving about.

This strikes me as gilding the lily to a certain degree. It can't hurt, but I've never had much trouble with scopes walking about. I guess it depends on how badly you want that extra little bit of assurance that all is as it should be with your rifle.

Mike Baugh
March 13, 1999, 08:02 PM
I have lapped in several ring sets and the biggest advantage I have found is I can remove a scope and have no marks on the tube . It also keeps the rings from exerting uneven pressure on the scope tube . I have a 1" diameter piece of cold rolled steel rod 12" in length that I use with valve grinding compound to lap in the rings , coat the rod and push it through the rings back and forth while turning the rod , you would be surprised how far out a new set of quality rings can be when factoring in bases and receiver hole locations . I clean the rod and rings a couple times during this process also . Mike...

Michael Carlin
March 13, 1999, 11:13 PM
Lapping scope rings trues the rings to each other. The new rings may have been well machined, but when mounted on various (note the intent to imply differences) recievers of the same make they may not be perfectly aligned with each other.

This was one of the reasons that when I was young the one piece base was supposedly superior. It tended to limit the amount of misalignment that the gunsmith could induce in installing two piece base systems.

So what you ask?

This is very important, for if the tube is tweaked, kinked, or otherwise stressed, the internal adjustments will be "bound up" by the stresses. Imagine what would happen to any precision instrument that was twisted about its long axis. The amount of bind will adversely affect the repeatability of adjustment.

The best scopes in the world will not perform to their potential if their mount torques the tube, and binds up their internals.

Additionally, stresses applied to the tube tend to degrade the optical performance. Optimum optical performance requires that the optical centers of the elements (lens) be aligned. This is definitely not going to be true if we twist the scope out of shape squeezing it into misaligned rings.

Those of you who mount a scope on your 2+ minute of angle rifle to shoot deer at 100 yards, never "sight in" at any other range, and have not touched the adjustments of your scope for years may find all of this very boringly esoteric.

Those of you shooting any rifle any sight matches at 800, 900 and 1000 yards, as well as the silhouette shooters, and long range varminters/benchresters may consider this much more important.

Is lapping necessary? It depends. If your are installing a $40 scope on a $275 factory rifle to shoot factory loads at a large game animal at under 200 yards... probably not.

If you installing a $500 instrument on a rifle capable of using that level of precision due to its accuracy, it definitely is IMHO worth the limited expense and effort to do so.

Hope this helps.

Ni ellegimit carborundum esse!

Yours In Marksmanship


Rosco Benson
March 17, 1999, 09:25 AM
Sorry for the late reply, Rich. I've been out of town. I'm sorry to report that I've never bothered with ring lapping. There was an article on it in a fairly recent issue of Tactical Shooter magazine. As others have responded, the purpose is to ensure that the rings align with one another and to maximize the actual contact area between the rings and the scope tube. I would tend to put it into the same category as esoteric barrel break-in procedures, cryo-treatments, fire-lapping and other alchemy-smithing. If you THINK it'll help, then it probably will.

It seems to me that if the receiver is twisted or the holes mis-drilled in a manner that results in excessive stress being placed on the scope tube, you could lap 'til kingdom come and not help matters much. Sure, you would remove material where the misaligned ring encroached into the scopt tube's "space", but you won't ADD any metal to the areas out away from the tube.

If slippage of the scope within the rings is a concern, this can be prevented by putting a tiny dab of some sort of adhesive "goo" in each ring half. Ross Seyfried wrote this up a few years back. He used a product (from 3M, I think) that was meant to seal and insulate electrical terminals. I use a Duro product "Plastic Rubber", which is meant for repairing waders. A tiny dab...smaller than a match-head...in each ring half secures the scope nicely. The product I use cleans off the rings and scope tube easily.

There may be some objective benefit to lapping-in one's rings. It certainly hurts nothing. Still, it strikes me as falling into (to use a Cooperism) the "PII" category. That is, "Preoccupation with Inconsequential Increments".


Rich Lucibella
March 17, 1999, 12:44 PM
Thanks, guys. Great info.
Kevin McClung has provided the same viewpoint as you. He does use an adhesive to "bed" the rings, however.
Another Gunsmith has told me that most of Leupold's rings are ridged inside....therefore, lapping may be counterproductive.

I gues it is a matter pf psycho-comfort.