I've had my travails with scopes and scope mounts on both a 460 S&W Magnum and 500 S&W Magnum. Scopes that have malfunctioned include:
1. A Bushnell Trophy scope. Bushnell wouldn't fix or replace it saying it had "been abused."
2. Two T/C "Recoil Proof" scopes both of which were promptly replaced by T/C with new scopes.
3. A Leupold 2.5-8X VX III (fixed with no hassle by Leupold).
As far as the improper mounting theory goes I would say yes and no. Before I got in know, I used stuff like Thompson/Center's Duo-Rings which support the scope in only 2 places. This is fine with low recoil rounds but not with the 460 & 500 S&W Mags. The scopes weren't improperly mounted but the mounting wasn't sufficient for these high recoil rounds. All the mounts I used prior to going to SSK Industries' T'SOB mounts shot loose and the scopes, prior to using this mount with 4 rings always moved under recoil unless the scope was mounted with the turret against the front ring.
The scope failure with the Leupold 2.5-8X VX III was with the scope mounted in a 4 ring T'SOB mount on my 460 S&W Mag. and the mount, rings and scope had all been installed by SSK Industries. So, if that scope was improperly mounted, the mounting was done by J. D. Jones or his employes at SSK Industries.
I also had SSK Industries install a Leupold 2.5-8X VX III scope on my 500 S&W Mag. barrel in their 4 ring T'SOB mount. Prior to the use of this scope and mount, the accuracy was mediocre. Following the installation of this scope, I magically started getting 1 to 1.5 inch 3 shot groups at 100 yards off the bench.
Some may not know the reason S&W used a gain twist barrel (starting at 1:100 and going to 1:20 at the muzzle) on their 460 S&W Magnum barrels. It was because the torque without the gain twist was too hard on scopes. Obviously, T/C barrels don't have gain twist barrels and I'm not sure anyone makes scopes that will stand up long term to 460 & 500 S&W Mag. recoil. Something like a red dot or EOTech might stand up to recoil better but you can't get the accuracy with them that you can with a good scope. I would say, go with a scope made by a company who will fix or replace it when it breaks and expect to have some scope malfunctions until someone makes a more durable handgun scope.