Quoted:
Are .50 BMG rifles any harder on scopes than any other caliber / rifle combination?...
Yes, they are brutal on them.
I've seen all kinds of things fail on all brands.
It seems they will all fail eventually.
Sometimes you get a "lucky" scope that will last for 10,000 rounds
but most won't make it that far.
I've personally had my Nightforce, Leupold, Springfield, and Super-sniper fail.
Some cheap, some expensive, they all will eventually go it seems.
The best thing I can say is the better it is mounted, the longer it will last.
I like WIDE rings like D.D. Ross steel ones:
They give lots of support if you can find them
(the above picture is not my gun)
Lap the rings (with a ring lapping kit) to ensure even contact.
A bit if powdered rosin isn't a bad idea at the scope/ring interface.
This will allow the maximum life out of what you're running scope-wise.
If my life depended on it, I'd have a spare scope or BUIS.