Lapping, Aligning and Torquing scope rings
I had a couple of hours alone about 3 weeks ago and decided to align and lapp some scope rings. A couple of members have asked me to do this write-up, so here goes.
Why should scope rings be lapped, aligned and torqued?
Even a cheap scope is a precision optical device, so it needs to mounted straight (aligned), with rings and bases torqued correctly (so as to not crush the tube and put pressure on the lenses). Variable scopes, and higher power scopes are most susceptible to distortion caused by improperly aligned/lapped/torqued rings. Second Focal Plane variable scopes (American style where the crosshairs remain a constant size) are prone to suffer from a "shifting zero" as the power is changed, but much of that is due to lack of lapping/alignment. Low powered variables, and fixed power scopes are not as "twitchy", but their rings should still be lapped, aligned and torqued.
There are several variable surface dimensions involved when mounting a scope straight.
1.) The action. As actions are machined during manufacture the cutting tools get duller with every action made. Surface imperfections and variances from one to the next. Final polishing of the metal does more to change the final specs.
2.) Bases. The same machining process as above leaves each base with it's own variable tolerances.
3.) Rings. Rings are machined the same way, and have their own variances.
When all these variable surfaces are combined, it adds up to a set of rings that are almost always out of alignment to some degree once they are mated to a scope.
The quality/expense of the rifle/base/rings used does not matter. The worst set of rings I've ever seen were a set from a high end manufacturer, and the cost was almost $300. They were visibly off right out of the package by over a millimeter.
For the shooter who does not want to spend the money on the right tools to do this job, get your friends to pitch in. Then you can all help each other do your rifles. Every time I'm at the range with my tools, someone asks me to lapp their rings. They always try to pay me, so investing in the tools could end up a money making venture for most shooters. When I did this stuff for a living the going rate to lapp, torque and mount was $75-$150 depending on the amount of work needed. It can pay for your tools quickly.
But what if you check the alignment of the rings and they are perfectly straight? It is rare, but does happen. Well, the rings may be straight, but the bearing surfaces of the rings will have high spots and ridges. These need to be lapped away so the ring surface is smooth and fits flat against the tube of the scope. Any high spots on the inside of the ring surface can cause dents and pressure to the scope tube when the rings are tightened down.
My old FN Mauser in 7x57 needed to be lapped, so she is the model I used in this post.
Tools needed were:
Brownells screw driver kit (the best kit I've ever used)
Wheeler FAT Wrench torque wrench (not the most accurate on the market, but consistent and accurate enough when a 5 inch pound +/- is good enough)
Kokopelli Products accurizing kit (The best on the market, by far IMO)
Two small Stanley bubble levels
Tipton rifle cradle
I prefer one piece Picatinny or Weaver bases because they are designed to align themselves fairly well, and can be mounted and remounted with almost no loss in POI (Point Of Impact). But in this case I chose a rifle with a one piece Redfield/Leupold style base, which is very common. These are called "windage adjustable bases". The windage adjustment is in the large knobs on the sides of the rear ring. But the front ring fits very tightly into the base, so using the rear windage screws for adjustment purposes will bend the scope tube left or right, which leads to an "oval-ing" of the image through the scope. Don't use them for adjusting impact with the scope tube installed, and only for gross adjustments while setting up. Fine adjustments are done with the knobs on the scope.
Continued on next post...
Clean all the screws and screw holes with acetone (action, bases, rings, cross bolts, etc),
Torque the base screws down to about 30 inch lbs. For Weaver and Picatinny rings, torque the clamp screws or cross bolts to about 30-35 inch lbs. Once the ring bottoms are mounted to the base, check to make sure they are aligned, or close to being aligned (the Kokopelli front alignment bar has a hole in the end, and a rod that goes into the hole so that you can see how it lines up with the bbl.
The flat ends of the two alignment bars should line up (flat ends touching), edge to edge and be relatively straight. If more than a fingernail's width of overlap is evident, switch the rings around, turn them around, etc.
Find the position that aligns them best. Torque the rings down and get the lapping bar ready. The Kokopelli lapping bar has a groove machined into its surface to allow the lapping compound to stay in place during the lapping process.
The cheaper alignment bars with the pointy ends are terrible because points can line up, even if the rings are not aligned. Flat ends only line up when the rings are perfectly straight.
When you are finished with the lapping, the ring tops will be mated to the ring they are attached to, in the direction they are mounted, permanently. Mark the ring tops (front and rear), with an arrow pointing forward, using white out or a crayon, etc. I used black Sharpie marker, this time, because it was handy. "F" for front ring, "R" for rear, with an arrow pointing forward. This cleans off when you finish, leaving no permanent marks. If you ever need to remove the ring tops, mark them before you do so.
The actual lapping process is pretty straightforward.
Coat the lapping bar with a thin film of lapping compound, set it in the ring bottoms, and place the ring tops on. Put the screws in place and lightly tighten the screws (only til you feel resistance). I use the screwdriver bit between my thumb and forefinger to avoid over doing it. Once the rings are snug start working the lapping bar from side to side to take off the first edges.
At first there will be a decent amount of resistance. As moving the bar becomes easier, keep moving the from bar side to side and add in a front and back motion too; Almost a screwing motion. After 10-15 reps you will notice the bar moving easier due to material being removed from the rings. Lightly tighten the screws again until you feel resistance. If using rings with 4 or 6 screws tighten them in a cross pattern. It may only take 1/6th of a rotation on each screw, or less. Not very much. Do this a few times, keeping an eye on the gap between the top and bottom of the ring (where the screws go through) to make sure you don't remove too much material. You only need about 80% to 85% bearing surface on the ring surface.
After you have done 3-6 (or so) series of 10-15 reps, your rings should be ready to check.
Remove the lapping bar and wipe the rings clean with a rag. The lapping compound stains, so be careful. If you remove the ring tops to get the bar out, remember to pay attention to which is front/rear and which direction is pointing forward. Those rings are now mated in the place you set them originally.
The inside of the rings should now be a matte silver, and have a smooth feel with no ridges.
80%-85% of the surface is all that is needed to be flat and smooth for a good fit. If your rings look like that, you are good to go. Clean them up with acetone and use the Q-Tips to clean the screw holes. Get the threads on the screws and holes clean.
When you set your scope into the ring bottoms after lapping, it should freely slide forward and back with no "scraping" feel.
Adjust your scope for your eye relief (if you have questions about this please ask), and make sure the crosshairs are straight up and down. There is almost always a flat part across the action somewhere to use for this. The other flat part is the top of the adjustment knob, or cap.
It is easiest done if you have a clamping rest like the Tipton.
Then, tighten the ring top screws in a criss/cross pattern. Pay attention to the bubble levels as you tighten the screws as that will twist the scope out of the perpendicular.
Proper torque for aluminum rings is 10-15 inch lbs, while steel is 15-20 inch lbs.
It is a very simple process, but one that pays huge dividends.
How the alignment bars SHOULD line up before lapping. The knife tip is at the junction of the ends. These are close, but not perfect, but will be by the time we are finished.
Using the two levels to verify level spots. Notice the clean, post lapping ring surfaces.
A better shot of the steel rod used to align the rings with the centerline of the barrel.
A better shot of the "Pre-Lapped" rings showing the high spots and ridges. Very noticeable.
Good post. Well thought out and presented. My compliments.
M14 I like the way you did the lapping. Making sure to always be moving the lapping rod in a few different direction.
My problem with the other ways I had seen were the fact that the way they were lapping the rings would in reality cause them to be out of round. The one video the guy has the handle of the lapping rod between the rings and was just pushing on one side of the bar which we all know would apply a lot more pressure to the front opposite side of the bar causing that side to remove more metal. If you understand what I am saying.
Here this is a midwayusa video where they are just forcing the lapping bar back and forth.
You may convert me afterall.... LOL.... Great post.
Really well-done! Even epic!
And I agree that the comparison between the Kokopelli kit and the one you can get through Midway (by Wheeler) is night and day. The only problem is that the Kokopelli is expensive....and how many times am I actually going to use it? Perhaps a traveling set for FTF members to "check out" like a library book.......?
Also, you, Tango, and others have convinced me that, with few exceptions, a one-piece base is the way to go. Not only is it usually easier to mount the rings to, but it gives me much more of a sense that nothing is going to shift. The (Leupold and others) rings that have a dovetail front mount and the windage adjustment in the rear.....I just don't see how anyone could really trust them. IMO.
Thanks very much for that post, M14. :)
EXCELLENT post M14s! You really got it right and said/pics much better than I could have. I'm getting another digital camera to replace the 1 that Shihan & RSG gave me then my daughter accidentally broke.
Glad it made sense, Dan.
And Tango, if you had only seen the Wheeler kit before it makes sense that lapping would not be in your program. It is pretty weak. The Kokopelli kit is a must have item. Each one is hand made my a master machinist who also happens to be a precision rifle competitor.
And Lon, the kits will pay for themselves at the range. And the one you used was very easy to operate, right? And I wish you had been here to take the pics for me. Ha.
High praise from Bear will keep me in a good mood all day. Thanks!
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