 The resulting high-velocity fragments produced by either method are the main lethal mechanisms of these weapons, rather than the heat or overpressure caused by detonation, although offensive grenades are often constructed without a frag matrix.These casing pieces are often referred to as "shrapnel" by non-military media sources.The use of fragmentation in bombs dates to the 14th century, and appears in the Ming Dynasty text "Huolongjing".