Would you own and shoot a 50bmg that has a breach pressure up to 60,000 psi that uses a threaded cap next to your face to seal the breach? Christ I believe that the receiver doesn't have vents that at least will vent off pressure during a cartridge failure away from your face.
50bmg when shot produces a huge amount of gas when fired, you get what you pay for.
Still the bottom line is the owner was stupid and shot ammo out of a rifle that wasn't designed for it.
Hes a very lucky man to be alive.