The 34 mm main tube is somewhat a new standard meant for tactical rifle scopes. It is adopted by a lot of rifle scope manufacturers as it provides more space for elevation compared to the 30 mm tube. In order to mount the 34 mm rifle scope you need the mounting rings to fit this diameter.
The most important thing when mounting a rifle scope with rings is to be aware of the preassure needed to fasten the rings. Go over the limit and the structural integrity of the rifle scope will be compromised. Rings can also leave a visible mark if not tightent acordingly. The amount of torque should not exceed 2.2 Nm.
Rings with the diameter of 34mm are usually at least 20mm wide, while with tactical mounts the width can be as much as 32mm.
A lot of different manufacturers are putting their 34 mm products on the market. The 34 mm rings are manufactured by the following: EAW, MAK, Rusan, Recknagel,Contessa, Spuhr, Henneberger, Kozap, Leupold, Dentler and Madritsch.
Lapping is a process that is essentially lining two mounting rings perfectly to one-a-another. It is done with special cylinders that grind off the excess metal.
In the worst case scenario the axis that runs through the center of the rear ring does not completely match the axis that runs through the center of the front ring. For this reason the scope, if mounted into such rings is under unwanted structural stress. The most obvious problems that occurs due to this reason is less than perfect optical performance, tracking problems, the side focus mechanism can stop working and the point of impact groups can be dispersed.
If the ring is designed in the fashion of 1/3 base of the ring and 2/3 the top of the ring than lapping is not required as the design is plastic enough to bend slightly and adjust its shape to the scope tube. The same applies for ½ - 1/2 rings mounted on single piece base.
It may be a good idea to take in consideration to choose the 1/3 : 2/3 rings as they do not require additional lapping to be fitted properly. Or use a single piece mounting base.
Lapping is also not required with mono block mounts and all mounts made from one piece of material and alignment of both rings is usually perfect. It is also not required with high quality European mounts, since their tolerances are minimal.