Speculation is that Fusilier Hields was firing one of these:  http://youtube.com/watch?v=hN4GlNZB1-g

From the article: 

"Hields followed the trail of RPG-7 rocket-propelled grenades coming towards him and started firing grenades one at a time, trying to home in. “Then I switched to automatic fire,” he said. A grenade machine gun has a box with 32 grenade rounds. “I emptied a box onto that position and you could see all the dust and smoke flying about where they hit.

“After that no fire came back from that position and I moved on to the next one. One or two rounds until I got onto the target, and switch to automatic and empty the box.”"

Fusilier Hields on being wounded in that same firefight: 

"Hields said: “It turned out the bullet had smashed a rib and gone out of me again without touching any internal organs which was very lucky. It was just a flesh wound really.”"

Jesus jumping Jupiter.  Sighted in and emptied the box.  Twice.  No wonder the Taliban did their damnedest to kill him after that.