The seven Marines were working on range area known as John W. Bullard used for live-fire drills . But the deaths did n't occur under such live fire , a military source says . It 's possible that unexploded ordnance suddenly detonated , the source says . In this week , seven Marines were killed when a mortar round exploded in California .
The four Marines were working on range area known as Zulu Black used for live-fire drills . But the deaths did n't occur under such live fire , a military source says . It 's possible that unexploded ordnance suddenly detonated , the source says . In March , seven Marines were killed when a mortar round exploded in Nevada .