Its not the fact that the rings are horizontally split that can cause problems.
Whether the ring cap mounts on top of the ring body (the norm such as Seekins) or from the side (Vortex Viper, ARC) or diagonal, like (Spuhr) mdkes no difference.
The vertically split rings that have a seperate cap; a cap that only engages the scope tube and isnt pulling double duty as a rail clamp, is fine.
Example:
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The problem occurs with the vertically split rings that use each half to both hold the rail and the scope tube, such as the Leupold Rifleman and Warne Maxima.
I have some Warne Maxima rings and have been using them successfully for 8+ years on IOR and US Optics scopes.
I recommend for most, just use the horizontally split type, or seperate ring cap vertically split type (ARC, Spuhr, Vortex Viper)
If one already owns and wants to use the Warne Maxima type rings successfully, dont use the recommended torque values, especially on the bottom screws, it risks scope damage if your scope is on the MMC side of 30mm.
Its important that the scope tube be on the LMC (least material condition) side of its diameter tolerance. Example: A tube diameter of 29.98 mm would likely work fine, whereas a tube diameter of 30.02 mm could be problematic.
Also, its critical that the lower screw be torqued to its full torque value first, while the top screw is completely loose.
One of the ring halves has a lug that is designed to be torqued into contact with the other ring half first, before any torque is applied to the top screw. Once the bottom screw is torqued (about 15 lb-in is what ived used since day 1 with these rings) and the lug in the lower portion of the ring halve is in contact with the other half, the ID of ring is 30mm. Then, only after the bottom screws are tightened, the top screw can be tightened to 15 lb-in.
If the top screw is already tight, or even snug when you start tightening the bottom screw, then by the time you get the rings rail clamp into contact with the rail, your already crushing the scope tube.
I bought these rings a long time ago, and having a degree in Engineering, i immediately saw the potential for trouble. I looked them over, made some measurements, paid attention to the little things, and have been using them without issue for years.
That being said, there are better options out there!