As we were all banging away the range officer called an emergency cease fire, and everyone on all the ranges stopped and stepped back per orders. A helicopter was coming to land. WTF?
In a few minutes the LASD rescue helicopter roared on in and landed a hundred yards south of us, and then left in a few minutes.
The story I heard was that someone on a private range was shooting a modified .50 caliber machine gun (!?) that only shot semiautomatic, and somehow it fired with the bolt partially open. This isn't good, because then the hot gas from the propellant goes sideways as well as forwards, and one gets a faceful of fire and possibly chunks of stuff. Off he went to the hospital.
The story may be somewhat different, but this was from a range officer who should know.
This kind of accident is very, very rare. It's possible that the guy loaded his own ammunition and made a mistake, or that the gun itself had been modified poorly in some way. But it's also possible that it just broke. Scary stuff.
In any case I had a good time with my own unmodified, normal-powered stuff.