I did an informal lock-ring test a few years back to satisfy my curiosity. Setup was an ordinary resizing die with a large, flat base and a known good shellholder, both checked for tolerance stacking in the press by orienting each part in 90 degree increments and checking daylight at the contact point of the shellholder and die face under light pressure. An average was taken using .001" shim stock and the various lock rings tried under various force levels. There is enough flex in the system to force full contact but misalignment is obvious under light pressure. Press was a Lee Classic Cast turret press with the big ram, and every brand and era of lock ring I could find. I absolutely hate the RCBS rings because they stick hard against the turret plate and require a wrench to undo what was installed two-finger-tight. Also, I've had the damned things consistently back off during a long run of resizing to a precise datum dimension which is beyond frustrating when you realize it moved somewhere in the last 200 cases and you can never, ever, re-bump them exactly the same due to springback. The set screws in RCBS, Lyman, and Pacific dies invariably cock the ring catty-whompus and load on one edge which in turn loads the die threads in the press or turret crooked. The only locking ring worth a damn is the Forster split ring with the cross-screw because it actually draws up the threads to full mesh and stays square (as squarely as the ring threads are cut with the faces, anyway, which isn't perfect by the way but can be better one orientation than the other and can be blued and lapped true if you like). Unfortunately the Forster rings are too large to fit on a Lee four hole turret so they immediately go in the spare parts box or on things that I use in my single stage press like sizing dies and primer pocket swagers.
Back to the test. They all sucked in one way or another, some more than others, except the Lee locking rings. I got the least misalignment both initial and under load with the Lees. I know they're consistent because I size my .308 brass to exactly two thousandths longer then minimum headspace (2.331 at the datum, IIRC, sized to 2.333") and it's consistent to a tenth or two...and straight, even pressure.
I also discovered that sometimes Lee doesn't get their turret holes bored straight, either. Sometimes the crooked is egregious and clearly visible to the naked eye, something Lee fanbois need to keep an eye on.
Lee has a new design lock ring that takes a special tool they make out of plastic. The new tool reaches into the tight turret configuration easily but is flimsy junk. I plan to make an aluminum spanner with two steel pins that does the same thing. Usually finger-tight is enough but over time the o-rings creep into imperfections in the metal and stick enough to need a wrench to loosen.