Very interesting videos, and quite the assemblage of .600 Nitro Rifles.

I diverge from some shooters in that I always fire the right barrel/front trigger first. I grew up with SxS double trigger shotguns and this just feels natural.
I have never (well, never say never right?) had a double discharge, likely because on shotguns and big rifles I do not use the tip of my finger on the trigger as would a bench rest shooter but have the "meat" of my index finger on the trigger.

Your mileage may vary, and my 2¢ worth.
- Mike