How to lap scope rings

Many times when I get a question from a reader it will center around the lapping of a ring set prior to installing them. The lapping approach head is to make a better contact between the scope body and the inner area of the scope ring itself.

Sometimes when produced the rings will not be even in terms of inside will height, or the ring will retain imperfections that can damage the surface of the rifle scope itself.

One thing I have found when using many different brands of scope rings is the more I am will to pay for a ring set the less I need to worry about lapping them prior to installing them on a firearms receiver. At the price tag found on say a NightForce, if I need to lap scope rings something is very wrong here. (Just an example)

Move to the Chinese variants on scope rings and you had better have a lapping kit with a full set of grinding tools on hand. Again, the difference is in the quality of the product from square one.

Why Is It Important?

Here is what exactly happens when lapping is required. Say you buy a good looking set of a best scope ring but notice that they carry a series of fine raised lines above the surfaces of the inner band of material. These fine cut bands can be a bit uneven and as such can cause stress on even one small area of the scope tube.

Now, when you mount the scope and tighten down the top halves of your rings to the lower, pressure is generated against the scope tube and if not manufactured evenly with a smooth surface far more pressure will be induced in one place than another. Pressure generated by screwing down the rings can cause damage to the internal workings of the scope, or the tube housing itself at times. It can also cause scope alignment issues.

What You'll Need

What is required in the way of tools when lapping most scope rings? Assuming your not a gunsmith you are in general terms not equipped to take on the lapping produced with garden variety tools around the shop or home, and will need to buy at minimum a basic lapping kit.

Unless you’re going to do a great deal of scope transfer or general mounting work I would think twice about doing this job yourself. Say you are installing a deer rifle scope and don’t exact to be doing this any time soon again. Buying the required tools at that stage becomes more than just a bit questionable?

However, if you still want to learn how to lap scope rings on your own, here is the general approach taken by the do it yourself, homegrown gunsmith.

Alignment

If your going to take up installing scopes on a regular basis even for a small shop or friends the tools of the trade are easy to access through a gunsmith product supply, and consist of the following.

First of a scope base ring centering system is advised. This unit is a set of machined alignment tools that come to a point as they face each other on a jig mount. The cylinders, also referred to as a lapping rod, are screwed slightly forward toward each other and the very tip of each cylinder needs to align with the other perfectly straight.

Any deviating from this alignment and right off you know the scope bases have been mounted off center. In most cases, this is because of the base drill holes in the receiver rings and rear receiver assembly do not align correctly. While I have never seen this in custom built rifles I have seen it in some factory installs.

Polishing 

Assuming you have made this ring alignment check and everything is aligned, you're ready to proceed. The next step is to polish the top rings and bottom rings with a special compound that wears away any slightly raised surfaces, leaving you with a perfectly smooth set of rings.

You will need a lapping tool, which looks like a rifle bolt but at one inch or more sizing ( depends on the scope tube size) and should come in any kit. Now, with bottom rings locked onto the scope bases system that is also mounted on the rifle receiver, proceed with the following:

Place the lapping tool atop both lower ring assembly. With the tool in place set the top halves of your rings in place and screw them down but do not tighten, leaving room for the cylinder shaped tool to move back and forth across both forward and rear scope rings.

Using the lapping bar handle and a layer of abrasive compound made with silicon carbide, available through gunsmith supply house and applied directly to the ring set, move the tool back and forth across both rings gently.

This back and forth action will cause the lapping compound to wear away the high spots of the ring set and take off very small amours of metal if there is too much material on the inside surface of the rings, allowing it to take on a uniformly smooth surface area.

After the first adjustment and lapping of the rings, apply added polishing compound and tighten down the settings on the lapping cylinder once again. Just leave enough space so as to allow the tool to continue moving across the rings, as the idea is to take still another layer off the ring surface with gentle friction.

Avoid using too much polishing compound - it can get messy, and it's better to do a few touch up runs if necessary. If you're going to lap scope rings, it's important to take your time with the process.

Final Check

When this is completed several times the inner surface of the ring should be smooth and free of any abnormal dents or raised areas. Make a visual check after cleaning off the ring will shot places where bluing has been burnished away - that’s all ok in this case.

In most applications, the lapping system will return about 80 % to 90 % of the contact surface of the ring to 100% trueness to the wall of the scope sight.

If not sure or you find an area remaining that needs attention or gives some slight resistance when installing your scope, start the process all over again until you are pleased with the end results. Now you are free to install the scope and tighten the ring screws to confirm that everything looks and feels right.

How Much Difference Does it Make?

Now, I will again be clear to the reader. I don’t make up little stories, or back something that is snake oil. As I use high quality rings and shoot everything from 50 yards to over a mile on a regular basis, then run 10.000 words a month much of the time on those hands on field results, I can say for a fact that I have never lapped a scope ring. 

In most cases I will take a turn of Scotch tape on the scope’s body at the exact point my rings contact my scope. This will fill in any very minor dent or scratches inside the ring and to date now some hundreds of rifles and handguns later I have never had a single issue with damaged scopes or other related issues. 

I realize many bench rest shooters searching for perfection - the kind of accuracy necessary for that single rough hole in the paper with five shots - and those shooters could definitely benefit from learning how to lap scope rings.

Long range shooters now pushing for the three mile hits ( current fact) are in the hunt for anything that will shave an inch from a steel target group miles downrange, and a properly aligned, lapped scope mount can certainly help.

There is absolutely nothing wrong with lapping scope rings, but be sure you understand exactly why and what your getting into when you take up that task.

Parting Shots

I hope this article has helped you understand how to lap scope rings, what tools come in lapping kits and what else will be required, and what situations would benefit from the lapping process.

Is it worth investing in a steel lapping bar and polishing compound and spending hours making precise adjustments when you're using a cheap Chinese scope? Probably not.

But if you're chasing ultimate precision for your bench rest setup and want to make sure that your scope rings are perfectly aligned, smooth, and in proper shape for competition, it can certainly be a worthwhile process.