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...