Oops!
The technical term for such events is *A bad day at the office.* The high explosive grenade for an M79/XM148/M203 is supposed to be safe until the spin from the rifling gets it up to about 400 rpm, at which point it arms itself to detonate upon contact. The later M386 H.E. round differed from the earlier M381 and M441 rounds in that it had a longer arming distance of 14-28 meters compared to the 2-3 meters of the M381 and M441- which was probably what that poor goof with his new underbarrel XM148 was using.
But do not bet your life on the safing distance of any 40mm round, particularly in brush or woodland. It only has to go off too close to you only once.
But do not bet your life on the safing distance of any 40mm round...
As evidenced by Hanoi John’s first “Purple Heart” at Cam Rahn Bay.