I'll agree there are RTZ issues with switch barrels systems that incorporate additional equipment between the receiver and barrel. But I have a hard time faulting the set screw. I think the issue at hand is that the orientation of all components must be the exact same every time for RTZ to be consistent. When I say all components I mean barrel, helical collar, barloc collar, and reciever. In essence it is simply a stacking tolerances issue.
The set screw puts the Barloc in tension, depending on barrel location, helical collar orientation, and BarLoc orientation, I suspect that even though you are putting 90in-lbs on the BarLoc set screw every time, the tension in the system will be different, because something is not the same in the system.
I speculate this because after checking torque with 2 independent torque wrenches, 90in-lbs was never achieved at the same location of the set screw. Might be a quarter turn less, might be a quarter turn more. But it never lined up with the previous witness mark.
I too work in the oilfield, specifically in downhole drilling and measurements, and plenty of our tools use set screws to keep components in place. Most of the tools are rated to 30,000psi, 300deg F, vibration resistant to 6 g's.
Set screws seem to be working well for AI's barrel change system.