A court of inquiry into the death of an air force sergeant at Waiouru Military Camp in November has found that procedures for marking unexploded ammunition were not strictly followed.
But the court says it was unable to determine the exact reason for the explosion.
Andrew Forster was marking the site of an artillery shell for future disposal when it detonated, killing him instantly.
Land Component Commander Brigadier Dave Gawn says the court found the 46-year-old was using a rock to drive a stake into the ground.
He says there were lapses of judgment identified in not following correct procedures. Evidence collected by the court suggested that some form of energy was imparted during the marking of the shell, causing it to detonate.
In a statement, Karen Forster says the family accepts the findings of the inquiry into her husband's death.
She says it supports what the family believed, that he died as a result of an accident while fulfilling his duties.